feat: 4Hz fan control with gear/cruise-aware clamps; move hot signals to cereal

Fan control rework (thermald → 4Hz):
- DT_TRML 0.5s → 0.25s (thermald loop + fan PID now at 4Hz)
- New clamp rules based on (gear, cruise_engaged, standstill):
    parked                                → 0-100%
    in drive + cruise engaged (any speed) → 30-100%
    in drive + cruise off + standstill    → 10-100%
    in drive + cruise off + moving        → 30-100%
- thermald now reads gearShifter (via carState) and controlsState.enabled,
  passes them to fan_controller.update()
- Removed BENCH_MODE special case — new rules cover bench automatically
- Removed ignition-based branches — gear is the correct signal

System health overlay:
- Subscribed UI to peripheralState so we can read fanSpeedRpm
- Added FAN row: actual fan% (RPM / 65) to sit alongside LAG/DROP/TEMP/CPU/MEM.
  Shows the real fan output vs. what the PID is asking for.

Migrate hot signals from paramsMemory to cereal (frogpilotCarControl):
- Added latRequested @3 and noLatLaneChange @4 to FrogPilotCarControl schema
- controlsd sets FPCC.latRequested / FPCC.noLatLaneChange (send-on-change
  already gates the IPC)
- modeld reads from sm['frogpilotCarControl'] (added to its subscribers)
  instead of paramsMemory (saves ~20 file-read syscalls/sec)
- carcontroller reads from frogpilot_variables (set in-process by controlsd)
  instead of paramsMemory (saves ~100 file-read syscalls/sec in 100Hz path).
  Dropped carcontroller's now-unused Params instance and import.
- UI (ui.cc, onroad.cc) reads from sm['frogpilotCarControl'].noLatLaneChange
- Removed LatRequested and no_lat_lane_change param registrations + defaults

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -101,7 +101,7 @@ ClearPilot uses memory params (`/dev/shm/params/d/`) for UI toggles that should
 - **Python access**: Use `Params("/dev/shm/params")`
 - **Defaults**: Set in `manager_init()` via `Params("/dev/shm/params").put(key, value)`
 - **UI toggles**: Use `ToggleControl` with manual `toggleFlipped` lambda that writes via `Params("/dev/shm/params")`. Do NOT use `ParamControl` for memory params — it reads/writes persistent params only
-- **Current memory params**: `TelemetryEnabled` (default "0"), `VpnEnabled` (default "1"), `ModelStandby` (default "0"), `ScreenDisplayMode`, `DashcamState` (default "stopped"), `DashcamFrames` (default "0")
+- **Current memory params**: `TelemetryEnabled` (default "0"), `VpnEnabled` (default "1"), `ModelStandby` (default "0"), `ScreenDisplayMode`, `DashcamState` (default "stopped"), `DashcamFrames` (default "0"), `DashcamShutdown` (default "0")
 - **IMPORTANT — method names differ between C++ and Python**: C++ uses camelCase (`putBool`, `getBool`, `getInt`), Python uses snake_case (`put_bool`, `get_bool`, `get_int`). This is a common source of silent failures — the wrong casing compiles/runs but doesn't work.
 
 ### Building Native (C++) Processes
@@ -311,8 +311,7 @@ The OMX encoder (`selfdrive/frogpilot/screenrecorder/omx_encoder.cc`) was ported
 
 ### Params
 
-- `DashcamDebug` — when `"1"`, dashcamd runs even without car connected (for bench testing)
-- `DashcamShutdown` — set by thermald before power-off, dashcamd acks by clearing it
+- `DashcamShutdown` (memory param) — set by thermald before power-off, dashcamd acks by clearing it
 - `DashcamState` (memory param) — "stopped", "waiting", or "recording" — published every 5s
 - `DashcamFrames` (memory param) — per-trip encoded frame count, resets each trip — published every 5s
 
@@ -524,7 +523,7 @@ Power On
 
 ### ClearPilot Processes
 
-- `dashcamd` — raw camera dashcam recording (runs onroad or with DashcamDebug flag)
+- `dashcamd` — raw camera dashcam recording (always runs; manages its own trip lifecycle)
 
 ### GPS