Untrack stray worktree git-link; ignore .claude/worktrees/

The .claude/worktrees/feature-proposals worktree dir was accidentally
committed as a git-link. Remove it from tracking and gitignore the
worktrees directory so EnterWorktree scratch dirs are never tracked.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dpsiderius

.claude/worktrees/feature-proposals

@@ -6,3 +6,4 @@ gateway/.plotter-state.json
 gateway/.session.json
 .claude/settings.local.json
 *.FCBak
+.claude/worktrees/