feat: implement Trello board management

Add 5 board management tools extending the Trello client:
- trello_create_board — create a new board
- trello_rename_board — rename an existing board
- trello_archive_board — close/archive a board
- trello_open_board — re-open a closed board
- trello_board_details — view board with lists and members

Includes board name-to-ID resolution, 16 new tests, and spec doc.

Issue: #2

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) == 3
+        assert len(PLUGIN_TOOLS) == 8
         assert all(callable(t) for t in PLUGIN_TOOLS)