fix: rename migration to sequential 068, document convention

Renamed fc01_add_pending_task_lane → 068_add_pending_task_lane with
revision ID "068" and down_revision "067". Added migration naming
convention to CLAUDE.md to prevent future hex-hash migrations.

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

CLAUDE.md

@@ -211,6 +211,10 @@ cd frontend && npm run build
 # Database migrations
 cd backend && alembic upgrade head
 alembic revision --autogenerate -m "Description" --rev-id=NNN  # NNN = next sequential number
+# IMPORTANT: Migrations use sequential 3-digit IDs (001, 002, ..., 068, 069).
+# Check the latest: ls backend/alembic/versions/ | grep -E '^\d{3}_' | sort | tail -1
+# The revision ID and filename prefix MUST match (e.g., revision="068", file=068_description.py).
+# down_revision MUST point to the previous sequential number. Never use hex hash IDs for new migrations.
 
 # Access PostgreSQL
 docker exec -it patherly_postgres psql -U postgres -d patherly
@@ -415,7 +419,7 @@ gh run view <id> --json jobs --jq '.jobs[] | {name: .name, conclusion: .conclusi
 - **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`
+- **Schema change:** Update model → `alembic revision --autogenerate -m "desc" --rev-id=NNN` (NNN = next sequential number, e.g., 068 → 069) → review → `alembic upgrade head`
 - **New frontend API module:** Types in `types/` → export from `types/index.ts` → client in `api/` → export from `api/index.ts`
 
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