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

docs/backend/manage-boards-spec.md

@@ -3,7 +3,6 @@
 **Feature:** US: Manage Trello Boards
 **Issue:** #2
 **Branch:** `feature/manage-boards`
-**Doc:** 002
 
 ## Overview
 

docs/backend/trello-auth-spec.md

@@ -3,7 +3,6 @@
 **Feature:** US: Authenticate and Connect to Trello Account
 **Issue:** #1
 **Branch:** `feature/trello-auth`
-**Doc:** 001
 
 ## Overview