fix: resolve remaining CI failures — mapper FK mismatch and lint errors

Backend: Use string-form foreign_keys on SessionBranch.session to match
AISession.branches — mixed column-object vs string-expression caused
SQLAlchemy mapper initialization conflict.

Frontend lint fixes:
- Remove unused _escalateUploads, _intakeUploads destructured vars
- Remove unused _ticket, _chatId, _pinned parameters
- Replace empty interface with type alias (public-templates.ts)
- Suppress setState-in-effect in SimilarSessions, SidebarStatsBar,
  FlowPilotAnalyticsPage (intentional prop sync patterns)

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

frontend/src/types/public-templates.ts

@@ -37,7 +37,7 @@ export interface PublicGalleryResponse {
   domains: string[]
 }
 
-export interface PublicFlowDetail extends PublicFlowTemplate {}
+export type PublicFlowDetail = PublicFlowTemplate
 
 export interface PublicScriptDetail {
   id: string