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/passwords.py

@@ -21,6 +21,8 @@ import httpx
 from starlette.requests import Request
 from starlette.responses import JSONResponse
 
+from ..http import nextcloud_httpx_client
+
 if TYPE_CHECKING:
     from nextcloud_mcp_server.auth.storage import RefreshTokenStorage
 
@@ -252,7 +254,9 @@ async def provision_app_password(request: Request) -> JSONResponse:
 
     # Validate app password against Nextcloud
     try:
-        async with httpx.AsyncClient(timeout=NEXTCLOUD_VALIDATION_TIMEOUT) as client:
+        async with nextcloud_httpx_client(
+            timeout=NEXTCLOUD_VALIDATION_TIMEOUT
+        ) as client:
             # Use OCS API to verify credentials
             test_url = f"{nextcloud_host}/ocs/v1.php/cloud/user"
             response = await client.get(
@@ -380,7 +384,9 @@ async def delete_app_password(request: Request) -> JSONResponse:
     nextcloud_host = settings.nextcloud_host
 
     try:
-        async with httpx.AsyncClient(timeout=NEXTCLOUD_VALIDATION_TIMEOUT) as client:
+        async with nextcloud_httpx_client(
+            timeout=NEXTCLOUD_VALIDATION_TIMEOUT
+        ) as client:
             test_url = f"{nextcloud_host}/ocs/v1.php/cloud/user"
             response = await client.get(
                 test_url,