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/components/flowpilot/EscalateModal.tsx

@@ -16,7 +16,7 @@ interface EscalateModalProps {
 
 export function EscalateModal({ open, onClose, onEscalate, isProcessing, hasPsaTicket, sessionId }: EscalateModalProps) {
   const [reason, setReason] = useState('')
-  const [_escalateUploads, setEscalateUploads] = useState<FileUploadResponse[]>([])
+  const [, setEscalateUploads] = useState<FileUploadResponse[]>([])
 
   const handleSubmit = async () => {
     if (!reason.trim() || reason.trim().length < 5) return