fix: well-form NOSONAR suppressions (SonarCloud S7632/S7503)

The new decomposition modules used `# NOSONAR: reason` (colon form), which
SonarCloud flags as a malformed suppression comment (python:S7632) and which
fails to suppress the intended issue. Switch to the repo's bare `# NOSONAR`
convention with the rationale in a comment above, matching config.py and
auth/storage.py. This also lets the suppression silence python:S7503 (async
method without await) on the protocol-required no-op aclose stubs.

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

nextcloud_mcp_server/embedding/gateway_client.py

@@ -121,9 +121,11 @@ class GatewayProvider(OpenAIProvider):
     ):
         # AsyncOpenAI rejects an empty key; use a non-secret placeholder when
         # the gateway is unauthenticated. When a token provider is configured,
-        # the real Bearer is set on the client before each request.
+        # the real Bearer is set on the client before each request. The bare
+        # ``# NOSONAR`` silences the hard-coded-credential hotspot — this is a
+        # public placeholder string, not a secret.
         super().__init__(
-            api_key=_UNAUTHENTICATED_PLACEHOLDER,  # NOSONAR: placeholder, not a secret
+            api_key=_UNAUTHENTICATED_PLACEHOLDER,  # NOSONAR
             base_url=base_url,
             embedding_model=embedding_model,
             generation_model=None,  # gateway never generates