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/tdd.md

@@ -0,0 +1,7 @@
+---
+description: Test-driven development - write tests first, then implement
+---
+
+1. Read the skill file at `.agent/skills/test-driven-development/SKILL.md` using view_file
+2. Follow the TDD workflow exactly as described in the skill
+3. Write failing tests first, then implement code to make them pass