v0.3.0: Fix slash commands — add 9 workflows for Antigravity IDE

- Fix workflow frontmatter: remove 'name:' field (Antigravity uses
  filename as command name), add numbered steps format
- Add 6 new workflows: /debug, /tdd, /review, /verify, /finish-branch,
  /worktree — now 9 slash commands total
- Add workflow frontmatter validation to validate command
- Update check-pack.mjs for new workflow files
- Bump version to 0.3.0

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/.agent/workflows/worktree.md

@@ -0,0 +1,7 @@
+---
+description: Create an isolated git worktree for feature work
+---
+
+1. Read the skill file at `.agent/skills/using-git-worktrees/SKILL.md` using view_file
+2. Follow the worktree workflow exactly as described in the skill
+3. Create isolated git worktree with smart directory selection and safety verification