feat(integrations): add Google Health (Fit) integration with full permissions

OAuth2 flow with all 11 Google Fitness scopes (activity, body, sleep,
heart rate, nutrition, location, blood glucose/pressure/temperature,
oxygen saturation, reproductive health). Stores access + refresh tokens;
auto-refreshes on expiry.

GoogleHealthSignalSource fetches steps, sleep sessions, active minutes,
calories, and heart rate from the Fit aggregate + sessions APIs. Signals
flow into both the tip orchestrator and the health-vitals pre-compute
agent, which generates prompt snippets about step progress, sleep
deficit, sedentary time, and elevated heart rate.

Signal.kind extended with 'health'; IntegrationProvider extended with
'google-health'. Agent compute signal mapping enriched to include source,
kind, and all features so health-vitals can filter its own signals.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ml/agents/registry.py

@@ -16,6 +16,7 @@ from .momentum import MomentumAgent, MANIFEST as MOMENTUM_MANIFEST
 from .time_of_day import TimeOfDayAgent, MANIFEST as TIME_OF_DAY_MANIFEST
 from .recent_patterns import RecentPatternsAgent, MANIFEST as RECENT_PATTERNS_MANIFEST
 from .focus_area import FocusAreaAgent, MANIFEST as FOCUS_AREA_MANIFEST
+from .health_vitals import HealthVitalsAgent, MANIFEST as HEALTH_VITALS_MANIFEST
 
 _REGISTERED: list[tuple[BaseAgent, AgentManifest]] = [
     (OverdueTaskAgent(), OVERDUE_TASK_MANIFEST),
@@ -23,6 +24,7 @@ _REGISTERED: list[tuple[BaseAgent, AgentManifest]] = [
     (TimeOfDayAgent(), TIME_OF_DAY_MANIFEST),
     (RecentPatternsAgent(), RECENT_PATTERNS_MANIFEST),
     (FocusAreaAgent(), FOCUS_AREA_MANIFEST),
+    (HealthVitalsAgent(), HEALTH_VITALS_MANIFEST),
 ]
 
 # Sanity check — agent_id and manifest.id must agree, otherwise the registry