deploy: add build_sha visibility for precise drift detection

Make /health report the precise git SHA the container was built from,
so 'is the live service current?' can be answered without ambiguity.
0.2.0 was too coarse to trust as a 'live is current' signal — many
commits share the same __version__.

Three layers:

1. /health endpoint (src/atocore/api/routes.py)
   - Reads ATOCORE_BUILD_SHA, ATOCORE_BUILD_TIME, ATOCORE_BUILD_BRANCH
     from environment, defaults to 'unknown'
   - Reports them alongside existing code_version field

2. docker-compose.yml
   - Forwards the three env vars from the host into the container
   - Defaults to 'unknown' so direct `docker compose up` runs (without
     deploy.sh) cleanly signal missing build provenance

3. deploy.sh
   - Step 2 captures git SHA + UTC timestamp + branch and exports them
     as env vars before `docker compose up -d --build`
   - Step 6 reads /health post-deploy and compares the reported
     build_sha against the freshly-built one. Mismatch exits non-zero
     (exit code 6) with a remediation hint covering cached image,
     env propagation, and concurrent restart cases

Tests (tests/test_api_storage.py):
- test_health_endpoint_reports_code_version_from_module
- test_health_endpoint_reports_build_metadata_from_env
- test_health_endpoint_reports_unknown_when_build_env_unset

Docs (docs/dalidou-deployment.md):
- Three-level drift detection table (code_version coarse,
  build_sha precise, build_time/branch forensic)
- Canonical drift check script using LIVE_SHA vs EXPECTED_SHA
- Note that running deploy.sh is itself the simplest drift check

219/219 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/dalidou/docker-compose.yml

@@ -9,6 +9,15 @@ services:
       - "${ATOCORE_PORT:-8100}:8100"
     env_file:
       - .env
+    environment:
+      # Build provenance — set by deploy/dalidou/deploy.sh on each
+      # rebuild so /health can report exactly which commit is live.
+      # Defaults to 'unknown' for direct `docker compose up` runs that
+      # bypass deploy.sh; in that case the operator should run
+      # deploy.sh instead so the deployed SHA is recorded.
+      ATOCORE_BUILD_SHA: "${ATOCORE_BUILD_SHA:-unknown}"
+      ATOCORE_BUILD_TIME: "${ATOCORE_BUILD_TIME:-unknown}"
+      ATOCORE_BUILD_BRANCH: "${ATOCORE_BUILD_BRANCH:-unknown}"
     volumes:
       - ${ATOCORE_DB_DIR}:${ATOCORE_DB_DIR}
       - ${ATOCORE_CHROMA_DIR}:${ATOCORE_CHROMA_DIR}