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/api/webhooks.py

@@ -10,7 +10,6 @@ All endpoints require OAuth bearer token authentication via UnifiedTokenVerifier
 
 import logging
 
-import httpx
 from starlette.requests import Request
 from starlette.responses import JSONResponse
 
@@ -20,6 +19,8 @@ from nextcloud_mcp_server.api.management import (
     validate_token_and_get_user,
 )
 
+from ..http import nextcloud_httpx_client
+
 logger = logging.getLogger(__name__)
 
 
@@ -57,7 +58,7 @@ async def get_installed_apps(request: Request) -> JSONResponse:
             raise ValueError("Nextcloud host not configured")
 
         # Create authenticated HTTP client
-        async with httpx.AsyncClient(
+        async with nextcloud_httpx_client(
             base_url=nextcloud_host,
             headers={"Authorization": f"Bearer {token}"},
             timeout=30.0,
@@ -129,7 +130,7 @@ async def list_webhooks(request: Request) -> JSONResponse:
             raise ValueError("Nextcloud host not configured")
 
         # Create authenticated HTTP client
-        async with httpx.AsyncClient(
+        async with nextcloud_httpx_client(
             base_url=nextcloud_host,
             headers={"Authorization": f"Bearer {token}"},
             timeout=30.0,
@@ -210,7 +211,7 @@ async def create_webhook(request: Request) -> JSONResponse:
             raise ValueError("Nextcloud host not configured")
 
         # Create authenticated HTTP client
-        async with httpx.AsyncClient(
+        async with nextcloud_httpx_client(
             base_url=nextcloud_host,
             headers={"Authorization": f"Bearer {token}"},
             timeout=30.0,
@@ -286,7 +287,7 @@ async def delete_webhook(request: Request) -> JSONResponse:
             raise ValueError("Nextcloud host not configured")
 
         # Create authenticated HTTP client
-        async with httpx.AsyncClient(
+        async with nextcloud_httpx_client(
             base_url=nextcloud_host,
             headers={"Authorization": f"Bearer {token}"},
             timeout=30.0,