feat(api): argon2 password, idempotent admin seed, api-exception infra

Task 12 + Task 7 quality-review carryovers:

Part A - password hashing & controlled initial admin:
- src/auth/password.ts: hashPassword/verifyPassword over @node-rs/argon2
  (napi prebuilt, argon2id default); empty plain rejected at the door
- src/scripts/seed-admin.ts: idempotent admin seed (ADMIN_ACCOUNT/
  ADMIN_PASSWORD env, walk-up root .env load); existing account -> skip,
  never overwrites the password; no audit_logs (system op, no actor)
- pnpm seed script (build + node dist/scripts/seed-admin.js);
  .env.example dev defaults admin/admin-secret-change-me
- tests: test/password.spec.ts (5), test/seed.spec.ts real-DB idempotency (4)

Part B - Task 7 carryovers (all 8):
- ApiException(apiCode, message, httpStatus, details?) recognized first by
  the filter; unmapped-status rule: >=500 -> INTERNAL_ERROR + generic
  message, <500 -> VALIDATION_FAILED keeping original status (warn-logged)
- 5xx/INTERNAL_ERROR responses forced to generic message (leak fix)
- pino redact adds req.headers.cookie / res.headers.set-cookie
- x-request-id echo capped at 128 chars (fresh UUID beyond, no log)
- LOG_LEVEL validated against pino levels at module wiring -> fail fast
- shared/ constants (API_PREFIX), request-with-id, log-level (+spec)
- jest ts-jest reuses tsconfig.json; unit testMatch includes test/*.spec.ts
- build:watch script (no concurrently dep; dev = build:watch + node --watch)

api: 35 unit + 10 e2e tests green; root lint/typecheck/test green.

Co-Authored-By: Claude Code <noreply@anthropic.com>

services/api/package.json

@@ -5,7 +5,9 @@
   "description": "CN NestJS API service (P1a skeleton: bootstrap, /v1/health, request-id, error envelope)",
   "scripts": {
     "build": "tsc -p tsconfig.build.json",
+    "build:watch": "tsc -p tsconfig.build.json --watch",
     "start": "tsc -p tsconfig.build.json && node dist/main-cn.js",
+    "seed": "tsc -p tsconfig.build.json && node dist/scripts/seed-admin.js",
     "typecheck": "tsc --noEmit",
     "lint": "eslint .",
     "test": "jest",
@@ -15,6 +17,7 @@
     "@nestjs/common": "^10.4.6",
     "@nestjs/core": "^10.4.6",
     "@nestjs/platform-express": "^10.4.6",
+    "@node-rs/argon2": "^2.2.1",
     "@photo/contracts": "workspace:*",
     "@photo/db-cn": "workspace:*",
     "nestjs-pino": "^4.6.1",