fix(calendar): implement the OAuth and calendar-listing endpoints (#458)

* fix(calendar): implement the OAuth and calendar-listing endpoints

The plugin's config advertised a three-step setup and only step 1
existed. Step 3's picker fetched
/api/v3/plugins/calendar/list-calendars, which was never registered, so
Flask fell through to the global 404 handler and the user saw "Resource
not found" -- a message that names nothing and points nowhere. Step 2
had no endpoint at all, so even a working picker would have found no
token to list with.

Two routes, following the pattern the spotify and ytm plugins already
use for their own auth scripts:

  POST /plugins/calendar/authenticate    two-step Google OAuth
  GET  /plugins/calendar/list-calendars  calendars for the picker

The authenticate route drives calendar_registration.py, which the plugin
already ships and which was written expressly for this -- it reads a
redirect URL on stdin and prints one JSON object. It takes two calls
because a human has to visit Google in between; the script persists the
PKCE verifier from the first call for the second, without which the
exchange fails with "Missing code verifier".

The listing route reads the token directly rather than shelling out
again: the picker is interactive and a subprocess per click is slower
than the API call it would wrap. It refreshes an expired token in place,
sorts the primary calendar first, and drops entries with no id, which
could not be selected anyway.

Both name the plugin when it is not installed, rather than reproducing
the anonymous 404 that started this.

Verified against the live Google API on the dev rig: HTTP 200 with the
account's real calendars.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(calendar): one input for the auth code, and a louder warning

Two things reported after testing the flow.

There were two boxes and no way to tell which to use. The config
template's string branch dispatches widgets from an allow-list of names,
and anything missing from it falls through to a plain input type=text --
so the field rendered both the widget's own box and a stray one for the
same key. google-oauth is now on that list, which is all the widget ever
needed to render in place of the fallback rather than beside it.

And the warning that the redirect page fails to load was small grey text
under a link, which is where it is least likely to be read. It is now an
amber callout that leads with "The next page will fail to load. That is
expected." The failure lands at exactly the moment the user has to act
on it, and it looks precisely like the flow breaking rather than
working. The paste box is labelled too, rather than relying on a
placeholder that vanishes on focus.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(calendar): redact script diagnostics, and page the calendar list

Three findings from CodeRabbit, all valid.

Raw subprocess output was being returned to the client -- the script's
stderr on one path, and its own error payload on another. CodeQL flagged
the same line. That script handles OAuth client secrets and interpolates
exceptions into its messages, so either could carry a secret or a path.
Both now go to the log unredacted, where they are worth having in full,
and reach the client through a redactor.

That redactor already existed inside describe_exception, which only
takes exceptions. Split out as redact_text: an exception is not the only
thing worth returning, and a subprocess's stderr is just as capable of
quoting a token.

calendarList.list returns 100 entries per page by default, caps at 250,
and hands back a nextPageToken when there are more. Reading one page
would have hidden calendars from the picker with nothing to say the list
was cut short. It now pages, asking for 250 at a time, bounded at ten
pages so a malformed token cannot spin.

And a test helper was a lambda where ruff wants a def.

The five new tests fail against the previous commit.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(calendar): redact the last two raw exception interpolations

CodeQL flagged four exposure paths. Two were mine and genuinely raw: the
OSError from failing to spawn calendar_registration.py, which carries the
interpreter path and whatever the OS chose to say, and the ImportError
for the Google libraries, whose message named the missing module by
interpolating the exception directly. Both now go through
describe_exception, and the unredacted text goes to the log.

The other two are the repo-wide pattern from PR #448 -- 67 handlers on
main already return details=describe_exception(e), and these two new
handlers follow it. That function is the sanitizer: it strips URL
userinfo, auth headers and credential-shaped key=value pairs, collapses
to one line and caps the length. CodeQL's taint tracking cannot see a
sanitizer it has no model for, so it reports the flow regardless.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(calendar): announce status changes, name the paste box, drop a no-op

Three more from the review, all valid.

The status line is written after every async call -- the consent link is
ready, the exchange failed -- and was a plain paragraph, so a screen
reader was told none of it. It is a live region now.

The paste box had a visible label that was never associated with it, so
its only accessible name was the placeholder, which disappears on focus:
precisely when the value is being pasted. The label now points at the
input by id.

And a conditional in the test helper returned the same value from both
branches, which Ruff flags as RUF034. It was left over from making the
fake page; one page is all those cases need, and TestPagination builds
its own sequences.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* test(calendar): assert the accessibility relationships, not their parts

The previous assertions searched for role="status", aria-live, a label
`for` and an input `id` independently, so they passed whether or not
those belonged together. Two attributes on different elements announce
nothing, and a `for` that names something other than the input leaves it
just as anonymous.

Both attributes are now asserted on the status element itself, and the
label and input are checked to go through the same identifier rather
than merely both existing. Verified by mutation: a mismatched pair and a
displaced aria-live are both caught.

Reported by CodeRabbit, against tests I had written two commits earlier.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

web_interface/templates/v3/base.html

@@ -987,6 +987,7 @@
     <script src="{{ url_for('static', filename='v3/js/widgets/custom-feeds.js') }}" defer></script>
     <script src="{{ url_for('static', filename='v3/js/widgets/array-table.js') }}" defer></script>
     <script src="{{ url_for('static', filename='v3/js/widgets/google-calendar-picker.js') }}" defer></script>
+    <script src="{{ url_for('static', filename='v3/js/widgets/google-oauth.js') }}" defer></script>
     <script src="{{ url_for('static', filename='v3/js/widgets/day-selector.js') }}" defer></script>
     <script src="{{ url_for('static', filename='v3/js/widgets/time-range.js') }}" defer></script>
     <script src="{{ url_for('static', filename='v3/js/widgets/time-picker.js') }}" defer></script>

web_interface/templates/v3/partials/plugin_config.html

@@ -815,7 +815,7 @@
                     <i class="fas fa-info-circle mr-1"></i>
                     Changes in the file manager save immediately — no need to click Save Configuration.
                 </p>
-            {% elif str_widget in ['text-input', 'textarea', 'select-dropdown', 'toggle-switch', 'radio-group', 'date-picker', 'time-picker', 'slider', 'color-picker', 'email-input', 'url-input', 'password-input', 'font-selector', 'file-upload-single', 'plugin-file-manager'] %}
+            {% elif str_widget in ['text-input', 'textarea', 'select-dropdown', 'toggle-switch', 'radio-group', 'date-picker', 'time-picker', 'slider', 'color-picker', 'email-input', 'url-input', 'password-input', 'font-selector', 'file-upload-single', 'plugin-file-manager', 'google-oauth'] %}
                 {# Render widget container #}
                 <div id="{{ field_id }}_container" class="{{ str_widget }}-container"></div>
                 <script>