feat: 10fps daytime / 4fps night modeld + 2Hz GPS

Reduced-rate modeld path now branches on IsDaylight:
- daylight: skip 1/2 frames → 10fps (better model responsiveness when
  lighting gives the net more signal)
- night: skip 4/5 frames → 4fps (unchanged, conservative for power)

IsDaylight is already in /dev/shm (memory) via gpsd.py. Gated the
IsDaylight write on change — it flips twice a day, no reason to rewrite
every 30s. GPS polling bumped from 1Hz → 2Hz.

ModelFps publishes "10" / "4" / "20" so longitudinal_planner's dt and
FCW-threshold scaling (if re-enabled) still track actual rate.

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

system/clearpilot/gpsd.py

@@ -159,6 +159,7 @@ def main():
   params_memory = Params("/dev/shm/params")
   last_daylight_check = 0.0
   daylight_computed = False
+  prev_daylight = None  # CLEARPILOT: gate IsDaylight write on change
   print("gpsd: entering main loop", file=sys.stderr, flush=True)
 
   while True:
@@ -205,7 +206,10 @@ def main():
           last_daylight_check = now_mono
           utc_now = datetime.datetime.utcfromtimestamp(fix["timestamp_ms"] / 1000)
           daylight = is_daylight(fix["latitude"], fix["longitude"], utc_now)
-          params_memory.put_bool("IsDaylight", daylight)
+          # CLEARPILOT: gate on change — daylight flips twice a day, don't rewrite every 30s
+          if daylight != prev_daylight:
+            params_memory.put_bool("IsDaylight", daylight)
+            prev_daylight = daylight
 
           if not daylight_computed:
             daylight_computed = True
@@ -221,7 +225,7 @@ def main():
             params_memory.put_int("ScreenDisplayMode", 0)
             cloudlog.warning("gpsd: auto-switch to normal (sunrise)")
 
-    time.sleep(1.0)  # 1 Hz polling
+    time.sleep(0.5)  # 2 Hz polling
 
 
 if __name__ == "__main__":