feat: implement asset catalog database foundation (BAT-001, REQ-009/011/014)

Asset Catalog Model Implementation (BAT-001):
- Introduce assets table with UUID PK, symbol UNIQUE, markets TEXT[] array
- Define MarketCode enum (KRX, NXT, SOR, NASDAQ, NYSE, UPBIT, BITHUMB)
- Add Asset domain model with catalog properties
- Implement asset CRUD protocols in portfolio_repository
- Add PostgreSQL asset CRUD operations with GIN index on markets

Portfolio Model Refactoring (REQ-011):
- Add portfolios.asset_id UUID FK to assets(asset_id) ON DELETE RESTRICT
- Remove portfolios.symbol and portfolios.market columns
- Update Portfolio domain model to reference asset_id instead of symbol/market
- Refactor all portfolio queries to JOIN assets catalog
- Update all repository methods to use asset references

Data Migration (REQ-014):
- Create 20260519_0017 Alembic revision for assets table creation
- Create 20260519_0018 Alembic revision for atomic data migration:
  * Extract unique symbol combinations from portfolios
  * Aggregate markets using ARRAY_AGG(DISTINCT market)
  * Populate assets catalog with extracted data
  * Update portfolios.asset_id to reference new assets
  * Remove legacy symbol/market columns in single transaction
- Implement migration with rollback support

Requirements Approved (REQ-001~008):
- REQ-001~008 transitioned from Proposed to Approved
- Complete tag model requirement set with implementation readiness

New Requirements Approved (REQ-009~015):
- REQ-009: assets table schema (approved, included in BAT-001)
- REQ-010: admin asset catalog CRUD (approved, future BAT-002)
- REQ-011: portfolios asset_id FK (approved, included in BAT-001)
- REQ-012: portfolio create catalog validation (approved, future BAT-002)
- REQ-013: GET /v1/assets token branching (approved, future BAT-002)
- REQ-014: portfolios data migration (approved, included in BAT-001)
- REQ-015: asset catalog baseline docs (approved)

Code Changes:
- app/domain/models.py: Add Asset model, MarketCode enum, Portfolio asset_id FK
- app/repositories/portfolio_repository.py: Define asset CRUD protocol
- app/repositories/postgres.py: Implement asset operations with full CRUD
- app/api/v1_assets.py: Remove symbol/market direct references
- app/cli/commands/portfolio.py: Update portfolio commands for asset references
- app/schemas/portfolio.py: Update portfolio schema with asset_id
- All portfolio operations throughout codebase: Use asset references

Testing:
- Add test_asset_catalog.py for asset CRUD operations
- Verify REQ-009 AC-1~5 (asset catalog creation, lookup, uniqueness)
- Verify REQ-011 AC-1~5 (FK constraint, portfolio asset reference)
- Verify REQ-014 AC-1~6 (migration atomicity, data correctness, rollback)
- Update existing tests for asset model usage

Documentation:
- Create BAT-001 batch documents (planning, design, implementation, verification)
- Update dcy-001 with implementation details and confirmed architecture
- Add 8 new requirement documents (REQ-009~015)
- Update docs/discovery/index.md with batch entry

Impact:
- Database: assets catalog table, portfolios refactored to reference assets
- Migration: 2 new Alembic revisions (0017 assets, 0018 portfolio migration)
- API: Symbol/market now accessed through asset references
- CLI: Portfolio commands require asset reference pattern
- All existing portfolio data preserved and correctly migrated

docs/srs/Data/req-009_assets-table-schema.md

@@ -0,0 +1,109 @@
+# REQ-009: assets 테이블 스키마 도입
+
+- Status: Approved
+- Type: Data
+- Priority: High
+- Owner: Justin Ko
+
+## Intent
+- admin이 거래 가능한 종목을 중앙 관리할 수 있도록 `assets` catalog 테이블을 신규 도입한다.
+- 기존 `portfolios` 테이블에 혼합된 asset 정의(symbol, market)를 독립 엔티티로 분리하여 "자산"과 "포지션" 개념을 명확히 구분한다.
+
+## Requirement
+- `assets` 테이블을 신규 생성한다: `asset_id UUID PK`, `symbol TEXT NOT NULL UNIQUE`, `markets TEXT[] NOT NULL DEFAULT '{}'`, `display_name TEXT`, `status TEXT NOT NULL DEFAULT 'active'`, `created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()`, `updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()`.
+- `assets.markets` 컬럼에 GIN 인덱스(`idx_assets_markets_gin`)를 생성한다.
+- 시장 코드 허용 값을 Python Enum `MarketCode`(KRX, NXT, SOR, NASDAQ, NYSE, UPBIT, BITTHUMB)로 `app/domain/models.py`에 정의한다. API 수신 시 대문자 정규화 후 Enum 검증을 수행한다. DB CHECK constraint는 사용하지 않는다.
+- `app/domain/models.py`에 `Asset` 도메인 모델(asset_id, symbol, markets, display_name, status, created_at, updated_at)을 추가한다.
+- `app/repositories/portfolio_repository.py` Protocol에 asset CRUD 메서드(`get_asset_by_id`, `get_asset_by_symbol`, `list_assets`, `insert_asset`, `update_asset`)를 선언한다.
+- `app/repositories/postgres.py`에 위 메서드의 Postgres 구현을 추가한다.
+
+## Acceptance Criteria
+1. Given Alembic migration 적용 후, When `assets` 테이블 스키마를 확인, Then `asset_id UUID PK`, `symbol TEXT NOT NULL UNIQUE`, `markets TEXT[] NOT NULL DEFAULT '{}'`, `display_name TEXT`, `status TEXT NOT NULL DEFAULT 'active'`, `created_at`, `updated_at` 컬럼이 존재한다.
+2. Given `assets` 테이블 존재, When 동일 `symbol`로 두 번 insert를 시도, Then UNIQUE constraint violation이 발생한다.
+3. Given `assets` 테이블 존재, When 인덱스 목록을 확인, Then `idx_assets_markets_gin` GIN 인덱스가 존재한다.
+4. Given `MarketCode` Enum 검증 로직, When 허용되지 않은 코드(예: 'UNKNOWN')를 전달, Then Enum 검증 오류가 반환된다.
+5. Given `MarketCode` Enum 검증 로직, When 소문자 'krx'를 전달, Then 대문자 정규화 후 `MarketCode.KRX`로 검증이 통과한다.
+
+## Impacted Area
+- Docs:
+  - docs/data-model.md — `assets` 엔티티 추가 (REQ-015에서 처리)
+- Modules:
+  - `migrations/versions/` — `assets` 테이블 생성 Alembic revision 신규 추가
+  - `app/domain/models.py` — `Asset` 도메인 모델, `MarketCode` Enum 추가
+  - `app/repositories/portfolio_repository.py` — asset CRUD Protocol 선언 추가
+  - `app/repositories/postgres.py` — asset CRUD Postgres 구현 추가
+- Tests:
+  - `tests/test_asset_catalog.py` (신규) — schema 존재 확인, UNIQUE constraint, GIN 인덱스, MarketCode Enum 검증
+
+## Notes
+- REQ-010(admin CRUD), REQ-011(portfolios 재설계), REQ-013(GET /v1/assets), REQ-014(migration) 모두 이 REQ 선행 구현을 필요로 한다.
+- NFR-2(성능): `assets JOIN portfolios` 쿼리 성능은 이 REQ의 GIN 인덱스와 REQ-011의 FK 인덱스로 커버한다. 구체적인 응답 시간 목표는 batch design 단계에서 정의한다.
+- `assets` 테이블은 Alembic으로만 관리한다(ensure_schema() 대상 아님). runtime-flows.md Alembic/ensure_schema 경계 규칙 준수.
+- Source: dcy-001 FR-1
+
+## Change Log
+
+### CHG-20260519-02
+- Date: 2026-05-19
+- Author: Justin Ko
+
+#### Change Summary
+- Status: Proposed → Approved
+
+#### Intent
+- 승인 게이트 통과: 필수 필드(Status/Type/Priority/Owner/Intent/Requirement/AC/Impacted Area/Change Log) 모두 충족, AC 구체성 확인 완료
+
+#### Acceptance Criteria Delta
+- No change
+
+#### Impacted Area Delta
+- No change
+
+#### Delivery Trace Delta
+- Batches:
+  - none (미정)
+- Releases:
+  - none (미정)
+
+#### Revalidation Impact
+- Reverification Needed: no
+- Existing Implementation Invalidated: no
+- Status Recommendation: promote-to-approved
+- Follow-up Action: batch 계획 편입
+
+### CHG-20260519-01
+- Date: 2026-05-19
+- Author: Justin Ko
+
+#### Change Summary
+- 최초 생성 — dcy-001 confirm-discovery 후 draft-req 실행
+
+#### Intent
+- dcy-001 FR-1을 Data REQ로 분리; assets 테이블 스키마, 도메인 모델, MarketCode Enum 정의
+
+#### Acceptance Criteria Delta
+- Added:
+  - AC-1~5 최초 작성
+
+#### Impacted Area Delta
+- Docs:
+  - docs/data-model.md — 최초 지정
+- Modules:
+  - migrations/versions/, app/domain/models.py, app/repositories/portfolio_repository.py, app/repositories/postgres.py — 최초 지정
+- Tests:
+  - tests/test_asset_catalog.py — 최초 지정
+
+#### Delivery Trace Delta
+- Batches:
+  - none (미정)
+- Releases:
+  - none (미정)
+
+#### Revalidation Impact
+- Reverification Needed: no
+- Existing Implementation Invalidated: no
+- Status Recommendation: keep-current
+- Follow-up Action: confirm-req 후 batch 계획 편입
+
+#### Validation Plan
+- pytest로 AC-1~5 검증; DB 스키마 검사는 SQLAlchemy Inspector 또는 PostgreSQL psql로 확인