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/client/__init__.py

@@ -4,7 +4,6 @@ import os
 from httpx import (
     AsyncBaseTransport,
     AsyncClient,
-    AsyncHTTPTransport,
     Auth,
     BasicAuth,
     Request,
@@ -13,6 +12,7 @@ from httpx import (
 )
 
 from ..controllers.notes_search import NotesSearchController
+from ..http import nextcloud_httpx_transport
 from .calendar import CalendarClient
 from .contacts import ContactsClient
 from .cookbook import CookbookClient
@@ -67,7 +67,7 @@ class NextcloudClient:
         self._client = AsyncClient(
             base_url=base_url,
             auth=auth,
-            transport=AsyncDisableCookieTransport(AsyncHTTPTransport()),
+            transport=AsyncDisableCookieTransport(nextcloud_httpx_transport()),
             event_hooks={"request": [log_request], "response": [log_response]},
             timeout=Timeout(timeout=30, connect=5),
         )