Fix all ruff linting errors

- Fix import ordering (isort)
- Remove unused imports
- Fix line too long (>100 chars)
- Fix variable naming (PIECES -> piece_chars)
- Fix bare except clause
- Remove unused variable

tests/test_ssh_server.py

@@ -1,9 +1,9 @@
 """Tests for SSH server functionality."""
 
-import asyncio
-import pytest
 from unittest.mock import AsyncMock, MagicMock, patch
 
+import pytest
+
 
 class TestShellMateSSHServer:
     """Test SSH server authentication."""
@@ -113,9 +113,10 @@ class TestChessBoard:
 
     def test_board_initialization(self):
         """Board should initialize with standard position."""
-        from shellmate.tui.widgets.board import ChessBoardWidget
         import chess
 
+        from shellmate.tui.widgets.board import ChessBoardWidget
+
         widget = ChessBoardWidget()
 
         assert widget.board.fen() == chess.STARTING_FEN
@@ -136,9 +137,10 @@ class TestChessBoard:
 
     def test_square_selection(self):
         """Selecting a square should show legal moves."""
-        from shellmate.tui.widgets.board import ChessBoardWidget
         import chess
 
+        from shellmate.tui.widgets.board import ChessBoardWidget
+
         widget = ChessBoardWidget()
 
         # Select e2 pawn
@@ -152,9 +154,10 @@ class TestChessBoard:
 
     def test_square_deselection(self):
         """Deselecting should clear legal moves."""
-        from shellmate.tui.widgets.board import ChessBoardWidget
         import chess
 
+        from shellmate.tui.widgets.board import ChessBoardWidget
+
         widget = ChessBoardWidget()
         widget.select_square(chess.E2)
         widget.select_square(None)
@@ -251,9 +254,10 @@ class TestIntegration:
     @pytest.mark.asyncio
     async def test_server_starts(self):
         """Server should start without errors."""
-        from shellmate.ssh.server import start_server
-        import tempfile
         import os
+        import tempfile
+
+        from shellmate.ssh.server import start_server
 
         # Create a temporary host key
         with tempfile.TemporaryDirectory() as tmpdir: