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/server/oauth_tools.py

@@ -11,7 +11,6 @@ import secrets
 from typing import Optional
 from urllib.parse import urlencode
 
-import httpx
 import jwt
 from mcp.server.auth.middleware.auth_context import get_access_token
 from mcp.server.auth.provider import AccessToken
@@ -24,6 +23,8 @@ from nextcloud_mcp_server.auth.storage import RefreshTokenStorage
 from nextcloud_mcp_server.auth.token_broker import TokenBrokerService
 from nextcloud_mcp_server.auth.userinfo_routes import _query_idp_userinfo
 
+from ..http import nextcloud_httpx_client
+
 logger = logging.getLogger(__name__)
 
 
@@ -69,7 +70,7 @@ async def extract_user_id_from_token(ctx: Context) -> str:
             "OIDC_DISCOVERY_URI",
             "http://localhost:8080/.well-known/openid-configuration",
         )
-        async with httpx.AsyncClient() as http_client:
+        async with nextcloud_httpx_client() as http_client:
             discovery_response = await http_client.get(oidc_discovery_uri)
             discovery_response.raise_for_status()
             discovery = discovery_response.json()