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>

.env.example

@@ -0,0 +1,14 @@
+# Template — copy to .env (chmod 600, gitignored) and fill in real values.
+# Used by sms/config.py (Settings, env_prefix=voipms_).
+
+# voip.ms REST API credentials (portal login email + API password from API Security)
+VOIPMS_API_USERNAME=you@example.com
+VOIPMS_API_PASSWORD=your-api-password
+
+# SHA-256 hash of the accepted client API key (raw key is NOT stored here).
+# Generate: python3 -c "import secrets,hashlib; k=secrets.token_urlsafe(32); print('KEY:',k); print('HASH:',hashlib.sha256(k.encode()).hexdigest())"
+VOIPMS_SMS_API_KEY_HASH=
+
+# Optional overrides
+VOIPMS_DIALING_MODE=nanpa
+VOIPMS_DAILY_LIMIT=100