fix: correct tool annotations to match ADR-017 conventions

- Add destructiveHint=True to collectives_remove_tag (matches "remove"
  keyword pattern in annotation tests)
- Change collectives_update_collective to idempotentHint=False (update
  operations are non-idempotent per project convention)

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

nextcloud_mcp_server/server/collectives.py

@@ -205,7 +205,7 @@ def configure_collectives_tools(mcp: FastMCP):
 
     @mcp.tool(
         title="Update Collective",
-        annotations=ToolAnnotations(idempotentHint=True, openWorldHint=True),
+        annotations=ToolAnnotations(idempotentHint=False, openWorldHint=True),
     )
     @require_scopes("collectives:write")
     @instrument_tool
@@ -422,7 +422,9 @@ def configure_collectives_tools(mcp: FastMCP):
 
     @mcp.tool(
         title="Remove Tag from Collective Page",
-        annotations=ToolAnnotations(idempotentHint=True, openWorldHint=True),
+        annotations=ToolAnnotations(
+            destructiveHint=True, idempotentHint=True, openWorldHint=True
+        ),
     )
     @require_scopes("collectives:write")
     @instrument_tool