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/app.py

@@ -3,6 +3,7 @@ import json
 import logging
 import os
 import queue
+import re
 import shutil
 import sys
 import subprocess
@@ -27,6 +28,7 @@ from src.plugin_system.health_monitor import PluginHealthMonitor
 
 _JOURNALCTL = shutil.which('journalctl')
 _SYSTEMCTL = shutil.which('systemctl')
+_VCGENCMD = shutil.which('vcgencmd')
 
 # Create Flask app
 app = Flask(__name__)
@@ -498,6 +500,37 @@ class _StreamBroadcaster:
                         except queue.Full:
                             pass
 
+def _get_power_status():
+    """Check Raspberry Pi under-voltage/throttling status via vcgencmd.
+
+    Returns a dict of decoded flags, or None on non-Pi platforms (no
+    vcgencmd) or if the call fails for any reason. See:
+    https://www.raspberrypi.com/documentation/computers/os.html#get_throttled
+    """
+    if not _VCGENCMD:
+        return None
+    try:
+        result = subprocess.run(
+            [_VCGENCMD, 'get_throttled'], capture_output=True, text=True, timeout=2
+        )
+        match = re.search(r'0x([0-9a-fA-F]+)', result.stdout)
+        if not match:
+            return None
+        bits = int(match.group(1), 16)
+        return {
+            'under_voltage_now': bool(bits & 0x1),
+            'freq_capped_now': bool(bits & 0x2),
+            'throttled_now': bool(bits & 0x4),
+            'soft_temp_limit_now': bool(bits & 0x8),
+            'under_voltage_occurred': bool(bits & 0x10000),
+            'freq_capped_occurred': bool(bits & 0x20000),
+            'throttled_occurred': bool(bits & 0x40000),
+            'soft_temp_limit_occurred': bool(bits & 0x80000),
+        }
+    except (subprocess.SubprocessError, OSError, ValueError) as e:
+        app.logger.warning("vcgencmd get_throttled failed: %s", e)
+        return None
+
 # System status generator for SSE
 def system_status_generator():
     """Generate system status updates"""
@@ -544,7 +577,8 @@ def system_status_generator():
                 'cpu_percent': cpu_percent,
                 'memory_used_percent': memory_used_percent,
                 'cpu_temp': cpu_temp,
-                'disk_used_percent': 0
+                'disk_used_percent': 0,
+                'power': _get_power_status()
             }
             yield status
         except Exception as e: