feat: REQ-002/REQ-010 implementation — assets.tag_ids column + GET /v1/assets admin catalog (BAT-012)

- REQ-002 scope redefinition: portfolios.tag_ids → assets.tag_ids UUID[] column with GIN index
- REQ-010 augmentation: GET /v1/assets redesigned as admin catalog endpoint (admin-only, no token_type branching)
- Asset tagging infrastructure: tag_ids column, archived flag synthesis for inactive tags, list_assets N+1 optimization
- DB migration 20260521_0023: assets.tag_ids UUID[] NOT NULL DEFAULT '{}', idx_assets_tag_ids_gin
- Test suite: 17 new test cases for assets.tag_ids + GET /v1/assets AC-9~12 (362 tests total)
- Documentation: runtime flows, release baseline, batch verification all updated
- BAT-012 added to REL-001 Included Batch and marked release-candidate

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

docs/batches/index.md

@@ -19,3 +19,4 @@
 | BAT-009 | standard | release-candidate | REQ-025, REQ-026, REQ-027, REQ-028 | dcy-003 | [bat-009](./bat-009_20260521_v1-portfolios-crud-core/) |
 | BAT-010 | standard | release-candidate | REQ-030, REQ-031, REQ-032 | dcy-003 | [bat-010](./bat-010_20260521_v1-portfolios-sub-resources/) |
 | BAT-011 | standard | release-candidate | REQ-029 | dcy-003 | [bat-011](./bat-011_20260521_v1-portfolios-ledger-path-migration/) |
+| BAT-012 | standard | release-candidate | REQ-002, REQ-010 | dcy-001, dcy-002, dcy-003 | [bat-012](./bat-012_20260521_assets-tagging-and-admin-get-redefinition/) |