feat: implement Trello card management

Add 12 card management tools:
- trello_create_card — create a card on a list
- trello_card_details — view card with members, checklists, comments
- trello_update_card — update title, description, due date
- trello_move_card — move card to a different list
- trello_archive_card — archive a card
- trello_assign_member / trello_remove_member — member management
- trello_add_comment / trello_delete_comment — comments
- trello_add_checklist_item / trello_toggle_checklist_item / trello_delete_checklist_item

Also adds _delete() helper on TrelloClient for DELETE verbs.

73 total tests — all passing.

Issue: #4

tests/test_auth.py

@@ -325,5 +325,5 @@ class TestPluginMetadata:
         assert PLUGIN_NAME == "trello-plugin"
         assert isinstance(PLUGIN_DESCRIPTION, str)
         assert isinstance(PLUGIN_VERSION, str)
-        assert len(PLUGIN_TOOLS) == 12
+        assert len(PLUGIN_TOOLS) == 24
         assert all(callable(t) for t in PLUGIN_TOOLS)