feat(db): zero-downtime migration safety lint + db-migrate skill (#5041)

* feat(db): zero-downtime migration safety lint + db-migrate skill

Add scripts/check-migrations-safety.ts (check:migrations), a CI gate that
classifies statements in newly-added migrations into hard errors (rewrite),
annotate-to-acknowledge contract ops (`-- migration-safe: <reason>`), and
backfill warnings. Wire it into test-build.yml. Add the /db-migrate skill as
the judgment half (expand/contract phasing, app-code cross-ref, annotation
authoring).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(skills): run cleanup and db-migrate safety checks in /ship

* fix(db): address review — DROP INDEX lock symmetry, RENAME CONSTRAINT false-positive, alter-type literal match

- Non-concurrent DROP INDEX is now a hard error (ACCESS EXCLUSIVE lock), symmetric with CREATE INDEX; DROP INDEX CONCURRENTLY after a COMMIT passes clean. Removes the false-confidence annotate path.
- RENAME rule narrowed to RENAME COLUMN / table RENAME TO; RENAME CONSTRAINT and ALTER INDEX ... RENAME (metadata-only) no longer flagged.
- alter-type regex now requires TYPE to follow the column identifier, so it no longer matches TYPE inside a string default.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(db): enforce IF EXISTS on DROP INDEX CONCURRENTLY for replay idempotency

Symmetric with the CREATE INDEX CONCURRENTLY rule: a post-COMMIT DROP INDEX
CONCURRENTLY replays from the top on failure, so without IF EXISTS it aborts
re-dropping an already-gone index.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* improvement(skills): gate /ship cleanup on UI changes; default migration base to staging

- /ship runs /cleanup only when the diff touches UI code (.tsx or apps/sim/components|hooks|stores); the six passes are React-only.
- /ship runs check:migrations against origin/staging (the PR base).
- check:migrations default baseRef is now origin/staging instead of origin/main.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(db-migrate): add contract-pending TODO convention for deferred drops

Establishes a durable, greppable marker (`contract-pending(<precondition>): ...`)
left on the legacy column in schema.ts when an expand defers a drop, so the
contract phase doesn't rot. The outstanding-work list is `grep -rn contract-pending`;
the contract PR's `-- migration-safe:` annotation references the expand and deletes
the marker.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -29,6 +29,7 @@
     "check:zustand-v5": "bun run scripts/check-zustand-v5-selectors.ts",
     "check:react-query": "bun run scripts/check-react-query-patterns.ts --check",
     "check:utils": "bun run scripts/check-utils-enforcement.ts",
+    "check:migrations": "bun run scripts/check-migrations-safety.ts",
     "mship-contracts:generate": "bun run scripts/sync-mothership-stream-contract.ts",
     "mship-contracts:check": "bun run scripts/sync-mothership-stream-contract.ts --check",
     "mship-tools:generate": "bun run scripts/sync-tool-catalog.ts",