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/services/wix_service.py

@@ -225,9 +225,9 @@ class WixService:
                 'error': str(e)
             }
     
-    def import_image_to_wix(self, access_token: str, image_url: str, display_name: str = None) -> str:
+    def import_image_to_wix(self, access_token: str, image_url: str, display_name: str = None) -> Optional[str]:
         """
-        Import external image to Wix Media Manager
+        Import external image to Wix Media Manager.
         
         Args:
             access_token: Valid access token
@@ -235,7 +235,7 @@ class WixService:
             display_name: Optional display name for the image
             
         Returns:
-            Wix media ID
+            Wix media ID string, or None if import failed
         """
         try:
             result = self.media_service.import_image(
@@ -243,10 +243,15 @@ class WixService:
                 image_url,
                 display_name or f'Imported Image {datetime.now().strftime("%Y%m%d_%H%M%S")}'
             )
-            return result['file']['id']
-        except requests.RequestException as e:
-            logger.error(f"Failed to import image to Wix: {e}")
-            raise
+            if result and isinstance(result, dict) and 'file' in result:
+                media_id = result['file'].get('id')
+                if media_id:
+                    return str(media_id)
+            logger.warning(f"Image import returned unexpected result structure: {type(result)}")
+            return None
+        except Exception as e:
+            logger.warning(f"Failed to import image to Wix (non-fatal): {e}")
+            return None
     
     def convert_content_to_ricos(self, content: str, images: List[str] = None, 
                                  use_wix_api: bool = False, access_token: str = None) -> Dict[str, Any]:
@@ -276,7 +281,8 @@ class WixService:
     def create_blog_post(self, access_token: str, title: str, content: str, 
                         cover_image_url: str = None, category_ids: List[str] = None,
                         tag_ids: List[str] = None, publish: bool = True, 
-                        member_id: str = None, seo_metadata: Dict[str, Any] = None) -> Dict[str, Any]:
+                        member_id: str = None, seo_metadata: Dict[str, Any] = None,
+                        site_id: str = None) -> Dict[str, Any]:
         """
         Create and optionally publish a blog post on Wix
         
@@ -322,6 +328,7 @@ class WixService:
             tag_ids=tag_ids,
             publish=publish,
             seo_metadata=seo_metadata,
+            site_id=site_id,
             import_image_func=self.import_image_to_wix,
             lookup_categories_func=self.lookup_or_create_categories,
             lookup_tags_func=self.lookup_or_create_tags,