fix(api-v3): address CodeRabbit findings from the blueprint-split review

Fixes to the api_v3 package split (PR #553), one per finding verified
against the actual code:

- __init__.py: _redact_credentials only blanked scalar values under a
  credential-named key; a bare list of secrets under such a key (e.g.
  tokens: ["a", "b"]) passed through untouched, since the list branch
  recursed with no memory that its key looked like a credential. Nested
  dicts still walk normally (a documented, tested behaviour -- a container
  like secrets: {api_key: ..., note: ...} is a section name, not a value to
  blank outright), but any value reached under a credential-shaped key is
  now actually blanked.

- __init__.py: the OAuth helper script's raw stderr/stdout went to
  logger.error unredacted (CWE-532) right next to a comment claiming this
  was deliberate; the HTTP response already used the existing redact_text
  helper. Routed the log line through the same helper.

- __init__.py / starlark.py: the standalone Starlark manifest fallback
  (used when the plugin instance isn't loaded) read-modified-wrote
  manifest.json with no lock, unlike StarlarkAppsPlugin._update_manifest_safe
  (plugin-repos/starlark-apps/manager.py), which already holds an flock for
  the same file when the plugin is loaded. Added _starlark_manifest_lock,
  mirroring that pattern, and wrapped every standalone read-modify-write
  call site in it. The app-config update route also wrote config.json and
  the manifest as two separate, non-transactional writes (a second,
  distinct finding at the same call site); config.json is now rolled back
  if the manifest write that follows it fails.

- backup.py: restore options used bare bool() on values from the request,
  so {"restore_secrets": "false"} restored secrets anyway (bool("false") is
  True). Switched to the existing _coerce_to_bool helper already used for
  this exact purpose elsewhere in the package.

- config.py: an automated import-rewrite mangled four user-facing
  validation strings and their neighbouring comments -- "Invalid start
  time" had become "Invalid start _pkg.time" (and likewise for "end time")
  in both the schedule and dim-schedule per-day validation paths.

- display.py: `import _pkg.time as time_module` -- _pkg is a local alias
  for the package, not a real importable module, so this raised
  ModuleNotFoundError whenever a caller restarted an already-running
  display service via /display/on-demand/start, after the on-demand
  request was already written to cache. Fixed to `import time`. Audited
  the rest of the package for the same `_pkg.<module>` import mistake;
  every other `_pkg.` reference is a legitimate attribute read-through
  (`_pkg.time.time()`, `_pkg._get_starlark_plugin()`, ...), not a broken
  import statement.

- fonts.py: validate_file_upload's max_size_mb parameter is silently
  unused by that helper (it only checks filename/extension) -- the font
  upload route saved arbitrarily large files as a result. Added the same
  seek-and-check pattern already used for the sibling .star upload.

- wifi.py: two ad hoc, inconsistent bool coercions. POST
  /wifi/ap/auto-enable used bare bool(), so a JSON string "false" enabled
  it. POST /wifi/radio's enabled/force parsing recognized real bool and
  some strings but not int 1/0 (1 is True is False in Python). Factored one
  small _parse_bool_ish helper local to this file and used it at all three
  sites.

Not changed: the "unknown/misspelled restore option keys default to True"
half of the backup.py finding -- the file's own comment documents that a
missing key deliberately means "restore everything," matching the
already-existing JSON-parse-failure guard a few lines above it; only the
bool-coercion defect was a real bug.

Added or extended regression tests for every fix, following each area's
existing test conventions. Full suite: 4328 passed, 62 skipped, 2 failed
on both this branch and origin/main (missing tzdata package breaks two
timezone-alias tests in test_onboarding_checklist.py, unrelated to this
change) -- no new failures.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3bPMESe2TfrGvbs1ef9c5

test/web_interface/test_calendar_oauth_endpoints.py

@@ -363,6 +363,22 @@ class TestDiagnosticsAreRedacted:
         assert 'hunter2' not in error, error
         assert '<redacted>' in error, error
 
+    def test_script_stderr_is_redacted_in_the_log_too(self, tmp_path, caplog):
+        # Regression: the return value went through redact_text (asserted
+        # above), but the logger.error call right next to it logged `raw`
+        # verbatim -- a script that handles OAuth client secrets and can
+        # quote them in its stderr, landing unredacted in the log (CWE-532).
+        script = tmp_path / 'calendar_registration.py'
+        script.write_text(
+            'import sys\n'
+            'sys.stderr.write("boom client_secret=hunter2 more\\n")\n',
+            encoding='utf-8')
+        with caplog.at_level('ERROR', logger=mod.logger.name):
+            mod._run_calendar_registration(tmp_path, '')
+        logged = '\n'.join(r.getMessage() for r in caplog.records)
+        assert 'hunter2' not in logged, logged
+        assert '<redacted>' in logged, logged
+
     def test_a_failing_script_payload_is_redacted(self, client):
         (client.plugin_dir / 'credentials.json').write_text('{}', encoding='utf-8')
         (client.plugin_dir / 'calendar_registration.py').write_text(