feat: add fallback_steps to TypeScript types (Task 15)

Add optional fallback_steps field to ProceduralStep interface.
Add FallbackStepRecord interface and fallback_decisions field to Session.

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

frontend/src/types/session.ts

@@ -42,6 +42,14 @@ export interface TreeSnapshot extends TreeStructure {
   tree_type?: string
 }
 
+export interface FallbackStepRecord {
+  parent_step_id: string
+  fallback_step_id: string
+  completed_at: string | null
+  notes: string | null
+  outcome: 'resolved' | 'not_resolved' | 'skipped'
+}
+
 export interface Session {
   id: string
   tree_id: string
@@ -66,6 +74,7 @@ export interface Session {
   target_label?: string
   psa_ticket_id?: string | null
   psa_connection_id?: string | null
+  fallback_decisions?: FallbackStepRecord[]
 }
 
 export interface SessionCreate {

frontend/src/types/tree.ts

@@ -122,6 +122,7 @@ export interface ProceduralStep {
   section_header?: string
   reference_url?: string
   library_visibility?: 'team' | 'public'
+  fallback_steps?: ProceduralStep[]  // Optional fallback alternatives
 }
 
 export interface CustomProceduralStep {