Fix ruff lint errors across matrixbot (F401, F841, E402)

Remove unused imports: logging from bot.py and config.py, RoomMessageText/
UnknownEvent from callbacks.py, functools.partial and MAX_INPUT_LENGTH from
commands.py. Rename unused local variables to _ (resp in cmd_ping, symbols in
render_keyboard_plain, guesses_left in two wordle functions). Move wordle import
to top of commands.py to fix E402.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

matrixbot/wordle.py

@@ -317,7 +317,6 @@ def render_keyboard_plain(game: WordleGame) -> str:
             letter_states[letter] = max(letter_states.get(letter, -1), score)
 
     lines = []
-    symbols = {-1: " ", 0: "\u2717", 1: "?", 2: "\u2713"}
     for row in _KB_ROWS:
         chars = []
         for letter in row:
@@ -465,7 +464,7 @@ async def wordle_start_or_status(client: AsyncClient, room_id: str, sender: str,
     if sender in _active_games:
         game = _active_games[sender]
         if not game.finished:
-            guesses_left = 6 - len(game.guesses)
+            _ = 6 - len(game.guesses)
             grid_plain = render_grid_plain(game)
             kb_plain = render_keyboard_plain(game)
             plain = (
@@ -626,7 +625,7 @@ async def wordle_guess(
         return
 
     # Still playing — show grid + keyboard
-    guesses_left = 6 - len(game.guesses)
+    _ = 6 - len(game.guesses)
     grid_plain = render_grid_plain(game)
     kb_plain = render_keyboard_plain(game)
     plain = (