feat: add self-signed SSL certificate support for Nextcloud connections

Add NEXTCLOUD_VERIFY_SSL and NEXTCLOUD_CA_BUNDLE env vars to configure
TLS certificate verification for all outbound Nextcloud connections.
Centralizes SSL config via a new HTTP client factory (http.py) used by
all 27 Nextcloud-bound call sites, including API clients, OIDC endpoints,
OAuth flows, and health checks.

Closes #560

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextcloud_mcp_server/auth/keycloak_oauth.py

@@ -18,6 +18,8 @@ from urllib.parse import urlencode, urlparse
 
 import httpx
 
+from ..http import nextcloud_httpx_client
+
 logger = logging.getLogger(__name__)
 
 
@@ -107,7 +109,7 @@ class KeycloakOAuthClient:
     async def _get_http_client(self) -> httpx.AsyncClient:
         """Get or create HTTP client"""
         if self._http_client is None:
-            self._http_client = httpx.AsyncClient(timeout=30.0)
+            self._http_client = nextcloud_httpx_client(timeout=30.0)
         return self._http_client
 
     async def close(self) -> None: