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>

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`