Support Custom $CLAUDE_CONFIG_DIR

[eabrouwer3]

Summary

ucode hardcodes the Claude config directory to ~/.claude and ignores the
CLAUDE_CONFIG_DIR environment variable that Claude Code itself supports:

ucode/src/ucode/agents/claude.py

Lines 43 to 44 in 6d238e6

	CLAUDE_CONFIG_DIR = Path.home() / ".claude"
	CLAUDE_SETTINGS_PATH = CLAUDE_CONFIG_DIR / "ucode-settings.json"

Impact

I keep two Claude accounts on the same machine — a personal one in ~/.claude
and a work one in ~/.claude-work — and set CLAUDE_CONFIG_DIR automatically
based on the directory I'm in. Because ucode always reads and writes
~/.claude, its Claude configuration and validation steps fail whenever I'm
working under the work account.

Proposed fix

Resolve the config directory from the environment, falling back to the current
default:

CLAUDE_CONFIG_DIR = Path(os.environ.get("CLAUDE_CONFIG_DIR", Path.home() / ".claude"))

This matches Claude Code's own behavior and is backward compatible for anyone
who doesn't set the variable.