feat(analytics): add PSA activity logging and enhanced PSA metrics endpoint

- Log `note_posted` and `time_entry_posted` activities to `psa_activity_logs`
  after each successful PSA push in `psa_documentation_service.py`; errors
  are caught and logged without blocking the main push flow
- Add `PsaFunnel`, `PsaDailyTrend`, and `EnhancedPsaMetrics` Pydantic schemas
- Add `GET /analytics/flowpilot/psa-metrics?period=30d` endpoint (team_admin,
  rate-limited 15/min) returning time entry totals, push funnel
  (sessions → linked → doc pushed → time entry logged), and daily trend

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

backend/app/schemas/flowpilot_analytics.py

@@ -87,6 +87,27 @@ class FlowQualityResponse(BaseModel):
     needs_attention: list[FlowQualityRow]
 
 
+class PsaFunnel(BaseModel):
+    total_sessions: int
+    linked_to_ticket: int
+    doc_pushed: int
+    time_entry_logged: int
+
+
+class PsaDailyTrend(BaseModel):
+    date: str
+    entries: int
+    hours: float
+
+
+class EnhancedPsaMetrics(BaseModel):
+    total_time_entries: int
+    total_hours_logged: float
+    avg_hours_per_session: float
+    push_funnel: PsaFunnel
+    daily_trend: list[PsaDailyTrend]
+
+
 class FlowPilotDashboard(BaseModel):
     period: str
     total_sessions: int