feat: ContentGuardianAgent, onboarding UX, Team Activity action wiring, docs, agent help modal

ContentGuardianAgent consolidation:
- Merge 3 duplicate classes into single source in specialized/content_guardian.py
- Watchdog audit_committee() with heuristic scoring, coverage gaps, overlaps, alerts
- Remove misleading rejection_rate() helper; use acceptance_rate directly
- Integrate audit + alerts + trend signals into today_workflow_service.py

Team Activity page:
- QualityAuditPanel: health ring, per-agent critiques, coverage gaps, overlaps
- TrendSignalsPanel: opportunity cards with urgency/impact/coverage bars
- AlertBanner: persistent dismiss via POST /alerts/{id}/mark-read
- AgentHelpModal: dialog showing all 8 agents with descriptions, tools, schedule
- QualityAuditPanel action buttons: Fill gap -> /content-planning, Resolve overlap, View CTA on alerts/issues
- TrendSignalsPanel action buttons: Create content from this trend -> /blog-writer with trend context state

Onboarding system:
- Step 4 validation: no auto-pass via basic_ready; requires persona data or explicit progression
- Step 5 validation: logs warning on auto-pass without integration data
- OnboardingCompletionService: single DB session, transactional task creation, upsert pattern
- Business-without-website: nullable website_url on SIFIndexingTask and MarketTrendsTask
- DeepCompetitorAnalysisExecutor: 5-min timeout, 10-competitor cap, asyncio.wait_for
- Persona generation: async with 30s timeout, falls back to scheduler
- OnboardingProgressService.reset_onboarding(): resets session + pauses all DB tasks
- OnboardingControlService.reset_onboarding(): also cancels APScheduler jobs
- FinalStep TaskSchedulingPanel: shows scheduled/failed tasks after completion, 8s auto-redirect
- onboarding_completed agent activity event logged to feed

Documentation:
- docs-site/features/onboarding/: overview, steps, scheduler-tasks, technical-reference (4 pages)
- docs-site/mkdocs.yml: added Onboarding System nav section
- docs-site/features/sif-agents/: overview, agent-directory, committee-system, content-guardian (4 pages)
- docs-site/features/team-activity/: overview, quality-audit, trend-signals, alert-system (4 pages)
- docs-site/features/todays-workflow/: updated overview, technical-architecture, workflow-guide, api-reference

backend/models/website_analysis_monitoring_models.py

@@ -318,7 +318,7 @@ class SIFIndexingTask(Base):
     id = Column(Integer, primary_key=True, index=True)
 
     user_id = Column(String(255), nullable=False, index=True)
-    website_url = Column(String(500), nullable=False, index=True)
+    website_url = Column(String(500), nullable=True, index=True)
 
     status = Column(String(50), default='active', index=True)
 
@@ -331,7 +331,7 @@ class SIFIndexingTask(Base):
     failure_pattern = Column(JSON, nullable=True)
 
     next_execution = Column(DateTime, nullable=True, index=True)
-    frequency_hours = Column(Integer, default=48)  # Default 48 hours
+    frequency_hours = Column(Integer, default=48)
 
     payload = Column(JSON, nullable=True)
 
@@ -346,6 +346,7 @@ class SIFIndexingTask(Base):
 
     __table_args__ = (
         Index('idx_sif_indexing_tasks_user_site', 'user_id', 'website_url'),
+        Index('idx_sif_indexing_tasks_user_only', 'user_id'),
         Index('idx_sif_indexing_tasks_next_execution', 'next_execution'),
         Index('idx_sif_indexing_tasks_status', 'status'),
     )
@@ -387,7 +388,7 @@ class MarketTrendsTask(Base):
     id = Column(Integer, primary_key=True, index=True)
 
     user_id = Column(String(255), nullable=False, index=True)
-    website_url = Column(String(500), nullable=False, index=True)
+    website_url = Column(String(500), nullable=True, index=True)
 
     status = Column(String(50), default="active", index=True)
 
@@ -415,6 +416,7 @@ class MarketTrendsTask(Base):
 
     __table_args__ = (
         Index("idx_market_trends_tasks_user_site", "user_id", "website_url"),
+        Index("idx_market_trends_tasks_user_only", "user_id"),
         Index("idx_market_trends_tasks_next_execution", "next_execution"),
         Index("idx_market_trends_tasks_status", "status"),
     )