feat: Add custom step creation and backend support (Phase 3A: B.8-B.10, B.13)

Implements custom step creation forms and backend persistence:

Task B.8 - StepForm Component:
- Comprehensive form for creating custom steps
- Step type selection (decision/action/solution) with descriptions
- Required fields: title, instructions (markdown supported)
- Optional fields: help text, commands (dynamic array), category, tags
- Visibility control (private/team/public)
- Save to library checkbox
- Full validation with error display
- Dynamic command management (add/remove, label + command)
- Tag input with Enter key support

Task B.9 - CustomStepModal:
- Tabbed modal interface
- Tab 1: "Type My Own" - embeds StepForm
- Tab 2: "Browse Library" - embeds StepLibraryBrowser
- Handles both saved steps (API) and drafts (no save)
- Loading states during step creation
- Error handling with user feedback
- Returns Step or CustomStepDraft to parent

Task B.10 - Backend Custom Steps Support:
- Database migration: add custom_steps JSONB column to sessions
- Updated Session model with custom_steps field
- Updated SessionResponse schema with custom_steps
- Updated SessionUpdate schema to accept custom_steps
- Migration ready to run: 4cdb5cba1aff

Task B.13 - Session Types Updates:
- Added CustomStep and CustomStepDraft interfaces
- Updated Session interface with custom_steps field
- Updated SessionUpdate interface
- Exported step types from types/index.ts
- Full TypeScript support for custom step integration

Remaining tasks: B.11 (TreeNavigationPage integration), B.12 (Export)
Build tested successfully.

Related: Issues #8, #9, #10

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/types/index.ts

@@ -6,6 +6,7 @@ export * from './invite'
 export * from './tag'
 export * from './category'
 export * from './folder'
+export * from './step'
 
 // API response wrapper types
 export interface PaginatedResponse<T> {

frontend/src/types/session.ts

@@ -1,4 +1,5 @@
 import type { TreeStructure } from './tree'
+import type { Step, StepContent } from './step'
 
 export interface DecisionRecord {
   node_id: string
@@ -11,6 +12,21 @@ export interface DecisionRecord {
   attachments: string[]
 }
 
+export interface CustomStep {
+  id: string
+  inserted_after_node_id: string
+  step_data: Step | CustomStepDraft
+  timestamp: string
+}
+
+export interface CustomStepDraft {
+  title: string
+  step_type: 'decision' | 'action' | 'solution'
+  content: StepContent
+  category_id?: string
+  tags?: string[]
+}
+
 export interface Session {
   id: string
   tree_id: string
@@ -18,6 +34,7 @@ export interface Session {
   tree_snapshot: TreeStructure
   path_taken: string[]
   decisions: DecisionRecord[]
+  custom_steps: CustomStep[]
   started_at: string
   completed_at: string | null
   ticket_number: string | null
@@ -34,6 +51,7 @@ export interface SessionCreate {
 export interface SessionUpdate {
   path_taken?: string[]
   decisions?: DecisionRecord[]
+  custom_steps?: CustomStep[]
   ticket_number?: string
   client_name?: string
 }