fix: address third round of review feedback

Add BasicAuthLifespanContext Protocol to make the contract between
StdioContext and get_client() explicit and type-safe. Document why
mcp.get_context() is required for non-template resources. Add News
and Collectives to README Supported Apps table, fix transport default.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/context.py

@@ -1,6 +1,7 @@
 """Helper functions for accessing context in MCP tools."""
 
 import logging
+from typing import Protocol, runtime_checkable
 
 from httpx import BasicAuth
 from mcp.server.fastmcp import Context
@@ -14,6 +15,17 @@ from nextcloud_mcp_server.config import get_settings
 logger = logging.getLogger(__name__)
 
 
+@runtime_checkable
+class BasicAuthLifespanContext(Protocol):
+    """Protocol for lifespan contexts that carry a shared NextcloudClient.
+
+    Implemented by :class:`~nextcloud_mcp_server.stdio.StdioContext` and
+    the single-user lifespan context in ``app.py``.
+    """
+
+    client: NextcloudClient
+
+
 async def get_client(ctx: Context) -> NextcloudClient:
     """
     Get the appropriate Nextcloud client based on authentication mode.
@@ -59,7 +71,7 @@ async def get_client(ctx: Context) -> NextcloudClient:
         return await _get_client_from_login_flow(ctx, lifespan_ctx.nextcloud_host)
 
     # BasicAuth mode - use shared client (no token exchange)
-    if hasattr(lifespan_ctx, "client"):
+    if isinstance(lifespan_ctx, BasicAuthLifespanContext):
         return lifespan_ctx.client
 
     # OAuth multi-audience mode (has 'nextcloud_host' attribute)