feat: add Nextcloud Collectives app support (#621)

Implement MCP tools for the Collectives wiki/documentation app, enabling
agentic workflows for team knowledge base management.

16 tools covering collectives, pages, tags, search, and trash:
- Read: list collectives, list/get pages (with WebDAV content), search,
  list tags, list trashed pages
- Write: create/update collective, create/move/trash/restore pages,
  set emoji, create/assign/remove tags

Includes Docker hook for app installation, OCS API client with envelope
unwrapping, Pydantic models, unit tests (16), and integration tests (10).

Closes #621

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

nextcloud_mcp_server/app.py

@@ -117,6 +117,7 @@ from nextcloud_mcp_server.observability.metrics import (
 )
 from nextcloud_mcp_server.server import (
     configure_calendar_tools,
+    configure_collectives_tools,
     configure_contacts_tools,
     configure_cookbook_tools,
     configure_deck_tools,
@@ -1274,6 +1275,7 @@ def get_app(transport: str = "streamable-http", enabled_apps: list[str] | None =
         "webdav": configure_webdav_tools,
         "sharing": configure_sharing_tools,
         "calendar": configure_calendar_tools,
+        "collectives": configure_collectives_tools,
         "contacts": configure_contacts_tools,
         "cookbook": configure_cookbook_tools,
         "deck": configure_deck_tools,