Add static API-key auth, dockerize service, publish façade docs

- sms/auth.py: verify_api_key dependency (Bearer/X-API-Key, SHA-256 hash
  compare via secrets.compare_digest, fail-closed 503 if no hash). All routes
  gated via a protected router; /health stays open for probes.
- config.py: new sms_api_key_hash setting (VOIPMS_SMS_API_KEY_HASH).
- Dockerfile + .dockerignore + docker-compose.yml: lean python:3.13-slim
  image; secrets injected via env_file, never baked in; host-localhost-only
  port mapping (SMS_PORT override); /health healthcheck.
- .env.example: committed template (placeholders only, no secrets).
- sms/docs/sms-facade.dokuwiki.txt: abstraction API reference (published to
  the apidoc wiki at voipms:sms-facade).
- README: Authentication section, Docker section, 401/503 error rows.

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

.dockerignore

@@ -0,0 +1,15 @@
+# Keep secrets and bloat out of the image build context.
+.env
+.env.*
+!.env.example
+.venv/
+venv/
+__pycache__/
+*.py[cod]
+.git/
+.claude/
+# Reference docs aren't needed at runtime.
+sms/docs/
+Dockerfile
+docker-compose.yml
+.dockerignore