feat: session sharing frontend (#76)

* feat: add session sharing types, API client, and utilities

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add SessionTimeline and ActionMenu reusable components

SessionTimeline extracts timeline/checklist rendering from SessionDetailPage
into a reusable component for both authenticated and public session views.
ActionMenu provides a dropdown action menu with keyboard/click-outside dismiss.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add ShareSessionModal and integrate into SessionDetailPage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add Share Progress popover to TreeNavigationPage

Replace the single "Copy for Ticket" button with a "Share Progress"
popover that offers three actions: Copy Progress Summary (existing PSA
export flow), Copy Share Link (auto-creates account-only share if
needed), and Manage Share Links (opens ShareSessionModal).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add public SharedSessionPage with tree preview

Add the public-facing shared session page at /share/:shareToken that
renders shared sessions without authentication. Includes error handling
for 401 (redirect to login), 403 (access denied), 404 (not found),
and 410 (expired). The page features a minimal header, session metadata,
SessionTimeline component, and a new SharedSessionTreePreview component
that renders the decision tree structure with the path taken highlighted.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add My Shares management page with nav link

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: address code review issues in session sharing

- Add useCallback for loadShares in ShareSessionModal (React hook deps)
- Use TreeStructure type instead of Record<string, unknown> for type safety
- Fix login redirect format to match LoginPage's expected state shape

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add focused tests for session sharing utilities and API

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: resolve tree_structure type compatibility for shared session views

- Use TreeStructure & Record<string, unknown> intersection for JSONB flexibility
- Add explicit cast in SharedSessionTreePreview for recursive node rendering

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: add session sharing learnings to CLAUDE.md

Add gotchas #12 (TreeStructure vs Tree types) and #13 (login redirect
state format), note about npm run build strictness, and public route
pattern to Common Tasks.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: procedural editor UX improvements

Add URL intake field type, fix variable name editing collapsing fields
(index-based keys/updates), auto-generate variable names by field type,
add section header as first-class step type, and simplify step editor
with "More Options" collapsible for advanced fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: allow section_header step type in validation, improve tag input

- Add 'section_header' to VALID_STEP_TYPES in backend validation so
  procedural flows with section headers can be published
- Replace procedural editor's inline tag input with TagInput component
  (supports autocomplete, Tab, comma, semicolon, and paste splitting)
- Add semicolon delimiter support to TagInput component

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: add type-aware routing for procedural flows

Centralizes tree navigation routing via getTreeNavigatePath helper.
Fixes all pages to route procedural sessions to /flows/:id/navigate
instead of /trees/:id/navigate. Adds safety redirect in troubleshooting
navigator and resume support in procedural navigator.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: remove unused index prop from IntakeFieldEditor

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -139,7 +139,7 @@ pytest --override-ini="addopts="
 # First time only: create test database
 docker exec -it patherly_postgres psql -U postgres -c "CREATE DATABASE patherly_test;"
 
-# Frontend build
+# Frontend build (IMPORTANT: stricter than tsc --noEmit — always use as final check)
 cd frontend && npm run build
 
 # Database migrations
@@ -222,6 +222,10 @@ markSaved()  // Clear isDirty BEFORE navigate()
 navigate(`/trees/${newTree.id}/edit`)
 ```
 
+**12. TreeStructure vs Tree types:** `TreeStructure` is for node structure only — it does NOT have `tree_type`, `name`, etc. Those are on `Tree`. JSONB tree snapshots need `TreeStructure & Record<string, unknown>` for extra fields.
+
+**13. Login redirect state format:** `navigate('/login', { state: { from: { pathname: '/path' } } })` — LoginPage expects `state.from.pathname` (object), NOT a plain string.
+
 ---
 
 ## RBAC & Permissions
@@ -260,6 +264,7 @@ navigate(`/trees/${newTree.id}/edit`)
 
 - **New endpoint:** Create in `endpoints/` → add to `router.py` → schema in `schemas/` → tests → frontend API client
 - **New page:** Create in `pages/` → add route in `router.tsx` → nav link in `AppLayout.tsx`
+- **New public route (no auth):** Add at top level in `router.tsx` alongside `/login`, `/register` — NOT inside the `ProtectedRoute`/`AppLayout` children.
 - **Schema change:** Update model → `alembic revision --autogenerate -m "desc"` → review → `alembic upgrade head`
 - **New frontend API module:** Types in `types/` → export from `types/index.ts` → client in `api/` → export from `api/index.ts`