Split the monolithic kugetsu script into modular components:
Modules created:
- kugetsu-config.sh - Config/env loading and global variables
- kugetsu-index.sh - Index.json read/write via JSON
- kugetsu-worktree.sh - Git worktree operations
- kugetsu-log.sh - Structured logging and notifications
- kugetsu-session.sh - Session create/fork/destroy logic
- kugetsu-queue-daemon.sh - Queue daemon subprocess
Main script (kugetsu) is now a thin dispatcher that sources all modules.
Acceptance Criteria:
- All existing commands work exactly as before
- Main script sources modules
- Each module is independently testable
Fixes#116
