Deliver BAT-003: daemon .env loading (REQ-010, minor-change)

DaemonConfig.from_env() now best-effort loads a .env file (find_dotenv
usecwd, load_dotenv override=False) so operators can manage daemon env
vars via .env, with real OS env taking precedence. Add python-dotenv
dependency, gitignore .env, ship .env.example, and add config tests
(load / OS-env precedence / absence regression / missing-DSN guard).

Verification: 78 passed, ruff clean, .env ignored + .env.example tracked,
and a .env-only DaemonConfig smoke. Processed via the minor-change fast
path: REQ-010 (Configuration) -> Implemented, BAT-003 (batch-lite,
no design) -> release-candidate.

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

docs/batches/bat-003_20260604_daemon-dotenv-config/verification.md

@@ -0,0 +1,23 @@
+# BAT-003 Verification
+
+- Status: confirmed
+- Batch: BAT-003
+
+## Acceptance Mapping
+- REQ-010:
+  - AC1 .env 로드 → `test_loads_values_from_dotenv` + 스모크(dsn/total/port). **PASS**
+  - AC2 OS env 우선 → `test_os_env_takes_precedence_over_dotenv`(override=False). **PASS**
+  - AC3 .env 부재 회귀 → `test_no_dotenv_uses_os_env_only` + `test_missing_dsn_raises`. **PASS**
+  - AC4 gitignore/.env.example → `git check-ignore`: `.env` ignored, `.env.example` trackable. **PASS**
+
+## Evidence
+- Test: `pytest tests/runtime/test_config_dotenv.py` 4 passed; 전체 78 passed; ruff clean.
+- Manual: `git check-ignore .env` → ignored, `.env.example` → trackable. `./.env` 단독 로드 스모크.
+
+## no architecture impact confirmed
+- batch-lite, planning Design Gate=no. 구조/인터페이스/런타임 흐름 변경 없음(기동 시 env 소스 추가뿐). baseline 문서 영향 없음 → 동기화 evidence 불요.
+
+## Result
+- Ready for Release: true
+- Blocking Issues:
+  - 없음.