feat(web-ui): detect and surface Raspberry Pi under-voltage/throttling (#383)

* feat(web-ui): detect and surface Raspberry Pi under-voltage/throttling

Adds a vcgencmd get_throttled check to the system-status SSE stream and
surfaces it in the web UI:

- A header badge (next to CPU/Memory/Temp) that stays hidden when healthy,
  turns red when under-voltage/throttling is happening right now, and
  yellow if it happened earlier this session but has since cleared.
- A dismissible top banner (same pattern as the update-available banner)
  that appears while under-voltage/throttling is actively occurring, with
  guidance to check the power supply. Re-appears on a fresh occurrence
  even if a previous one was dismissed.
- A "Power Supply" card on the Overview tab alongside CPU/Memory/Temp/
  Display Status.

Motivated by a real device showing intermittent brightness flicker that
turned out to be ~1 under-voltage event every 30-90s (visible live via
`vcgencmd get_throttled` and dmesg's "Undervoltage detected!" messages) --
there was no way to see this from the web UI, only by SSHing in.

Returns None on non-Pi platforms (no vcgencmd on PATH), matching the
existing guard pattern used for the CPU temperature read.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

* feat(web-ui): add power supply diagnostics detail to Tools tab

The header badge/banner/Overview card added in the previous commit only
show a collapsed "is it bad right now" signal. This adds a "Power Supply"
section to the Tools tab with the full 8-flag breakdown (under-voltage,
throttled, freq-capped, soft-temp-limit -- each split into "right now" vs
"occurred since boot") for actually troubleshooting a recurring issue,
plus a pointer to the README's power supply sizing guidance when something
is or was flagged.

Reuses the existing stats SSE stream (window.statsSource) rather than
adding a new endpoint -- the same payload already drives the header/
banner/Overview card, so this just listens for it too.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

* fix(web-ui): address review findings on power supply monitoring

- Overview card left its "--" placeholder forever on non-Pi platforms since
  the update only handled a truthy data.power. Now explicitly renders "Not
  available" with a neutral icon/color for that case.
- vcgencmd failures logged at debug, invisible in default remote log
  output. Bumped to warning to match the nearby systemctl failure logging.
- The banner/badge/card and the Tools summary line only looked at
  under_voltage_now/throttled_now (+ occurred), silently ignoring
  freq_capped_now/occurred and soft_temp_limit_now/occurred from
  _get_power_status() -- a Pi that's actively soft-thermal-limited or
  frequency-capped showed a green "OK" everywhere except the detailed
  flag table buried in Tools. All four surfaces now fold all four "now"/
  "occurred" flags into the same active/occurred state.
- The banner text was hardcoded to "Under-voltage detected..." even when
  the actual active condition was throttling/freq-capping/thermal limiting.
  Added _activePowerConditionLabels() (shared, non-module global scope) to
  build the banner/tooltip text from whichever flags are actually set.

Skipped: TTL-caching _get_power_status() to avoid "multiplying forks
across browser tabs" -- that premise doesn't hold against this codebase.
_StreamBroadcaster (its own docstring says as much) already runs exactly
one shared generator per tick regardless of client count, identical to
the uncached cpu_temp file-read two lines above it; there's nothing to
multiply.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

* fix(web-ui): address second round of review findings on power monitoring

- updatePowerStatus's falsy-power branch only hid power-stat, leaving
  power-warning-banner visible with stale text if _get_power_status()
  fails transiently. Now hides the banner too and resets the dismissed
  flag, same as the "not active" branch.
- The Tools tab's status badge (and the pre-existing dirty/clean badge
  right next to it) build class names like bg-${color}-100/text-${color}-800
  at runtime. This project hand-rolls its own Tailwind-named utility
  classes in app.css rather than running a real Tailwind build, and the
  light-mode base rules for bg-red-100/bg-yellow-100/bg-green-100/
  text-red-800/text-yellow-800/text-green-800 were simply never defined --
  only some had dark-mode overrides, which are no-ops without a base rule
  in light mode. Added the missing light-mode bases plus the two missing
  dark-mode overrides (bg-yellow-100/bg-green-100), fixing both badges.
- The "occurred earlier" tooltip was a hardcoded string regardless of
  which flag(s) actually fired. Generalized _activePowerConditionLabels()
  to take a suffix ('_now' or '_occurred') and reused it for both tooltips.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

* refactor(web-ui): move Power Supply status off the Overview tab

The Overview tab's "Power Supply" stat card duplicated what the Tools
tab's diagnostics section already shows (summary badge + full flag
breakdown), so drop the card and its now-dead JS rather than keep two
copies in sync. The header badge and warning banner (visible on every
page) are unaffected -- only the Overview-tab card is removed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

web_interface/static/v3/app.css

@@ -84,6 +84,8 @@
 [data-theme="dark"] .hover\:text-gray-700:hover { color: #e5e7eb; }
 [data-theme="dark"] .hover\:border-gray-300:hover { border-color: #6b7280; }
 [data-theme="dark"] .bg-red-100 { background-color: #450a0a; }
+[data-theme="dark"] .bg-yellow-100 { background-color: #422006; }
+[data-theme="dark"] .bg-green-100 { background-color: #022c22; }
 [data-theme="dark"] .text-red-700 { color: #fca5a5; }
 [data-theme="dark"] .hover\:bg-red-200:hover { background-color: #7f1d1d; }
 
@@ -137,6 +139,14 @@ body {
 .text-green-600 { color: #059669; }
 .text-red-600 { color: #dc2626; }
 
+/* Status badge chips (e.g. tools.html's dirty/clean and power-status badges) */
+.bg-red-100 { background-color: #fee2e2; }
+.bg-yellow-100 { background-color: #fef9c3; }
+.bg-green-100 { background-color: #dcfce7; }
+.text-red-800 { color: #991b1b; }
+.text-yellow-800 { color: #854d0e; }
+.text-green-800 { color: #166534; }
+
 .border-gray-200 { border-color: #e5e7eb; }
 .border-gray-300 { border-color: #d1d5db; }
 .border-gray-700 { border-color: #374151; }
@@ -1040,3 +1050,26 @@ button.bg-white {
 [data-theme="dark"] .update-banner-dismiss {
     color: #93c5fd;
 }
+
+/* Under-voltage / throttling warning banner */
+.power-warning-banner {
+    background-color: #fef2f2;
+    border-color: #fecaca;
+    color: #991b1b;
+}
+.power-warning-banner-dismiss {
+    color: #991b1b;
+    opacity: 0.6;
+}
+.power-warning-banner-dismiss:hover {
+    opacity: 1;
+}
+
+[data-theme="dark"] .power-warning-banner {
+    background-color: #450a0a;
+    border-color: #7f1d1d;
+    color: #fca5a5;
+}
+[data-theme="dark"] .power-warning-banner-dismiss {
+    color: #fca5a5;
+}