fix: align hooks declaration with current Claude Code schema

[n-dryer]

Summary

The plugin currently fails to load on recent Claude Code (Status: ✘ failed to load). Two small schema fixes:

• hooks/hooks.json — wrap the existing event map under a top-level "hooks": { ... } record. CC's hooks validator now requires this top-level key; without it, load fails with:

  hooks: Invalid input: expected record, received undefined

• .claude-plugin/plugin.json — drop the \"hooks\": \"./hooks/hooks.json\" line. CC now auto-loads hooks/hooks.json by convention, so declaring it explicitly causes:

  Duplicate hooks file detected: ./hooks/hooks.json resolves to already-loaded file ... The standard hooks/hooks.json is loaded automatically, so manifest.hooks should only reference additional hook files.

Behavior is unchanged — the same SessionStart hook still fires ensure-setup.sh.

Repro before the fix

$ claude plugin validate <plugin-dir>
✘ Found 1 error:
  ❯ hooks: Invalid input: expected record, received undefined

$ claude plugin list | grep -A 4 gstack
  ❯ gstack@...
    Status: ✘ failed to load
    Error: Hook load failed: [{"expected":"record","code":"invalid_type","path":["hooks"],"message":"Invalid input: expected record, received undefined"}]

After

$ claude plugin validate <plugin-dir>
✔ Validation passed

$ claude plugin list | grep -A 3 gstack
  ❯ gstack@...
    Status: ✔ enabled

Tested via a wrapper marketplace pointing at this branch, on Claude Code installed from the Mac desktop app. SessionStart hook still runs ensure-setup.sh end-to-end (Playwright Chromium download + browse binary build + compat symlink).

Test plan

• claude plugin validate <plugin-dir> → passes
• Install via marketplace → Status: ✔ enabled in claude plugin list
• Open a fresh CC session → SessionStart hook runs ensure-setup.sh, vendor/gstack/browse/dist/browse ends up built
• Skills (browse, plan-ceo-review, plan-eng-review, qa, retro, review, setup-browser-cookies, ship) appear in the session's available-skills list

🤖 Generated with Claude Code