Add validation and error handling for removing linked worktrees:
- validateRemoveWorktreeInput() — validates path is non-empty
- isMainRepository() — refuses removal of main repo root
- hasUncommittedChanges() — checks git status --porcelain output
- buildWorktreeRemoveCommand() — builds git worktree remove args
Wire up createRemoveWorktreeTool with full validation pipeline:
1. Validate input parameters (path)
2. Check if target is the main repo — refuse with prune suggestion
3. Check for uncommitted changes — refuse with stash/commit message
4. Run git worktree remove <path>
5. Surface git errors with helpful suggestions
