feat: REQ-005 assets table tag apply/remove SQL alignment (BAT-013)

- REQ-005 CHG-20260521-02 follow-up: clarify AC-1/AC-5 to target assets table
- Add append_asset_tag_id/remove_asset_tag_id on PostgresPortfolioRepository
- Replace internal calls in apply_asset_tag/remove_asset_tag routes (HTTP contract unchanged)
- 7 new regression tests: method existence, SQL target table, error branches, idempotency guard
- Update existing AC-1/AC-5 assertions to verify new methods + portfolios methods uncalled
- Documentation: runtime-flows.md flow body + change log; rel-001 includes BAT-013
- REQ-005 transition: Approved → Implemented (CHG-20260521-03) via BAT-013 verification
- Total tests: 362 → 369 passed

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/releases/index.md

@@ -8,4 +8,4 @@
 
 | REL ID | Profile | Status | Included Batch | Date | Doc |
 | --- | --- | --- | --- | --- | --- |
-| REL-001 | app-service | draft | BAT-001~012 | 2026-05-21 | [rel-001](./rel-001_20260521_v1-api-full-surface.md) |
+| REL-001 | app-service | draft | BAT-001~013 | 2026-05-21 | [rel-001](./rel-001_20260521_v1-api-full-surface.md) |