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

frontend/src/components/BlogWriter/BlogWriterUtils/PhaseContent.tsx

@@ -50,6 +50,8 @@ interface PhaseContentProps {
   onAngleSelect?: (angle: string) => void;
   selectedCompetitiveAdvantage?: string;
   onCompetitiveAdvantageSelect?: (advantage: string) => void;
+  introduction?: string;
+  onIntroductionUpdate?: (intro: string) => void;
 }
 
 export const PhaseContent: React.FC<PhaseContentProps> = ({
@@ -95,6 +97,8 @@ export const PhaseContent: React.FC<PhaseContentProps> = ({
   onAngleSelect,
   selectedCompetitiveAdvantage,
   onCompetitiveAdvantageSelect,
+  introduction,
+  onIntroductionUpdate,
 }) => {
   return (
     <div style={{ display: 'flex', flex: 1, overflow: 'hidden' }}>
@@ -173,8 +177,10 @@ export const PhaseContent: React.FC<PhaseContentProps> = ({
                 researchTitles={researchTitles}
                 aiGeneratedTitles={aiGeneratedTitles}
                 sections={sections}
+                introduction={introduction}
                 onContentUpdate={handleContentUpdate}
                 onSave={handleContentSave}
+                onIntroductionUpdate={onIntroductionUpdate}
                 continuityRefresh={continuityRefresh || undefined}
                 flowAnalysisResults={flowAnalysisResults}
                 sectionImages={sectionImages}
@@ -199,7 +205,7 @@ export const PhaseContent: React.FC<PhaseContentProps> = ({
             )}
           </>
         )}
-
+        
         {currentPhase === 'seo' && contentConfirmed && outline.length > 0 && outlineConfirmed && (
           <>
             {Object.keys(sections).length > 0 && Object.values(sections).some(content => content && content.trim().length > 0) ? (
@@ -211,8 +217,10 @@ export const PhaseContent: React.FC<PhaseContentProps> = ({
                 researchTitles={researchTitles}
                 aiGeneratedTitles={aiGeneratedTitles}
                 sections={sections}
+                introduction={introduction}
                 onContentUpdate={handleContentUpdate}
                 onSave={handleContentSave}
+                onIntroductionUpdate={onIntroductionUpdate}
                 continuityRefresh={continuityRefresh || undefined}
                 flowAnalysisResults={flowAnalysisResults}
                 sectionImages={sectionImages}