chore(db): no-op legacy migration 0002; gitignore QA audit scratch

The 0002_admin_password.sql migration referenced a 'users' table that
no longer exists — auth moved from Auth.js Credentials to Neon Auth
(Better Auth), which owns its own neon_auth.user schema.

The migration was being recorded in _migrations to skip, but a fresh DB
or new environment would fail with 'relation users does not exist'.
scripts/migrate.js already had an ensureTracked() repair path that
auto-marks 0002 applied when the users.password_hash column exists,
so legacy DBs still work. For fresh DBs, this rewrite replaces the
broken ALTER with a no-op SELECT 1, preserving the 0002 slot so
0003_*.sql onward numbering is unaffected.

Also add .gitignore entries for local-only QA artifacts:
- db/migrations/0000_qa_*.sql (Neon Auth stub for local audit)
- db/seeds/2026-qa-*.sql      (production-scale audit seed)
- docs/qa/                    (local audit plan/inventory/bugs)

These files should never apply to production (the migration stub
would conflict with real neon_auth.user; the seed is 1000s of rows).
Tracking progress in /tmp/refactor-routecomm.md.

db/migrations/0002_admin_password.sql

@@ -1,20 +1,17 @@
--- 0002_admin_password.sql
+-- 0002_admin_password.sql (no-op)
 --
--- Adds a `password_hash` column to `users` so the Auth.js Credentials
--- provider can verify email + password against the database.
+-- This migration slot is preserved for historical DB compatibility.
+-- The original content added a `password_hash` column to a legacy `users`
+-- table used by the old Auth.js Credentials provider. That table no longer
+-- exists — auth moved to Neon Auth (Better Auth), which manages its own
+-- `neon_auth.user` schema. See CLAUDE.md "Authentication & Authorization".
 --
--- Idempotent: uses `ADD COLUMN IF NOT EXISTS`. The column is nullable
--- because OAuth-only users (Google) never set a password.
+-- Production DBs that ran the original migration already have this filename
+-- recorded in `_migrations` and will skip it. Fresh DBs would otherwise
+-- fail on `ALTER TABLE users`; this no-op keeps the apply path clean while
+-- preserving the migration numbering (0003_*.sql onward is unaffected).
 --
--- The Credentials provider's `authorize` function is documented in
--- `src/lib/auth.ts` — it queries this column and runs `verifyPassword`
--- (see `src/lib/passwords.ts`) before returning the user.
+-- Do not reintroduce an `ALTER TABLE users` here — the table does not exist
+-- and Neon Auth owns user identity.
 
--- Transaction is managed by the migrate runner (scripts/migrate.js).
--- File kept small and re-runnable via IF NOT EXISTS on the ALTER.
-
-ALTER TABLE users
-  ADD COLUMN IF NOT EXISTS password_hash TEXT;
-
--- Update the updated_at trigger tracking — no new triggers needed since
--- `users` already has `set_updated_at` from migration 0001.
+SELECT 1;