Add Raspberry Pi health monitoring

Co-authored-by: Copilot <[email protected]>

PLAN.md

@@ -981,13 +981,33 @@ high-water mark plus the latest trip rather than loading the unbounded full hist
   markers, DTCs, and video data untouched. The deployed motion-aware logger then proved two
   consecutive stationary heartbeats were 60.02 seconds apart rather than five seconds.
 
-### Phase 19: Pi health monitoring card — 🚧 PLANNED
-**New phase, small and standalone - no dependencies.** CPU temperature, free disk space, uptime,
-and RAM usage are all cheap to read (`vcgencmd measure_temp`, `psutil`/`/proc` stats) and cheap to
-display, but currently invisible - the only way to notice a problem (thermal throttling in a hot
-car, an SD card filling up) today is to SSH in and check manually. Add a small backend endpoint
-and a dashboard card (built on the Phase 15 component set) surfacing these at a glance. Also
-feeds directly into Phase 20's alerting.
+### Phase 19: Pi health monitoring card — ✅ DONE
+Added a dependency-free `/api/health` endpoint and responsive dashboard card reporting CPU
+temperature, usable disk pressure/free bytes, RAM usage, human-readable uptime, and Raspberry Pi
+firmware power/throttling flags. Data comes from thermal sysfs, `/proc`, `shutil.disk_usage`, and
+`vcgencmd get_throttled`; individual unavailable sources are reported explicitly without hiding
+the remaining readings. The endpoint exposes structured current and historical flags for Phase
+20 alerts, plus warning/degraded/ok status. The browser refreshes every 30 seconds.
+
+**Implemented and verified 2026-08-09:**
+- Five focused tests cover memory parsing, missing memory fields, current/historical throttling
+  bits, malformed firmware output, and ext4 reserved-block-aware disk pressure. Local non-Pi
+  validation correctly reports thermal/firmware sources as unavailable while retaining disk,
+  memory, and uptime instead of failing the endpoint.
+- Removed the old browser-triggered thread that emitted uptime once per second indefinitely; the
+  health poll now provides uptime cheaply with the rest of the system snapshot.
+- Deployed uncommitted code to the real Pi. The API returned complete data with no source errors:
+  about 47-49°C, 19-20% RAM, 59% usable disk pressure with 22.8GB free, and roughly two hours
+  uptime during testing. SQLite/app service behavior remained active.
+- Real hardware monitoring immediately found an actionable condition: `vcgencmd get_throttled`
+  alternated between `0x50005` (current undervoltage and CPU throttling, both previously occurred)
+  and `0x50000` (historical occurrences after the current condition cleared). The dashboard
+  prominently distinguishes current warnings from prior events. The Pi power source/cable should
+  be corrected before sustained in-car use.
+- Browser-tested the real dashboard through `http://yaris.local/` at 390x844 and 1280x900:
+  all four metrics, warning state, timestamp, responsive columns, and 30-second data path rendered
+  without overflow or new console errors. Also fixed disconnected OBD speed showing `undefined`
+  and deferred offline map tiles until a real GPS fix, avoiding irrelevant placeholder requests.
 
 ### Phase 20: Alerts/notifications — 🚧 PLANNED
 **New phase - depends on Phases 13/17/19 existing first**, since it needs real data sources to