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>

sms/config.py

@@ -44,4 +44,13 @@ class Settings(BaseSettings):
         ge=0,
     )
 
+    sms_api_key_hash: str = Field(
+        "",
+        description=(
+            "Comma-separated SHA-256 hex hashes of accepted client API keys. "
+            "Generate a key, hash it (sha256), and store only the hash here — "
+            "the raw key is never persisted. Empty = fail-closed (503)."
+        ),
+    )
+
     timeout: float = Field(30.0, description="HTTP timeout in seconds.", ge=1.0)