remove legacy browser and verify skills

[brsbl]

Summary

• Removes the legacy standalone /browser and /verify skills.
• Removes their packaged agent-browser dependency.
• Updates active docs/workflows to route browser/Electron/UI checks through /test browser, /test electron, project-specific harnesses, or the host browser automation tool.
• Removes stale plugin registrations and old browser-session cleanup debt.

Changes

• Deletes skills/browser/** and skills/verify/**.
• Removes agent-browser from root package.json / package-lock.json.
• Removes deleted skill/agent registrations from .claude-plugin/marketplace.json.
• Removes /browser from CLAUDE.md and replaces README browser utility rows with /test/host-tool guidance.
• Updates /otto, /spec, and /test guidance so they no longer point at deleted standalone UI skills or their packaged CLI dependency.
• Removes stale browser.pid cleanup snippets from reset skills.

Dependabot / related PR cleanup

• Branch history is one cleanup-only commit on origin/main; no QA rewrite commits remain.
• There were no open Dependabot PRs for agent-browser or deleted skills/browser / skills/verify paths to close.
• Existing open Dependabot PRs for vite / picomatch are retained because they are still used by active test/summary tooling, not by the deleted legacy skills.
• No Dependabot config change is needed after removing agent-browser; future dependency PRs for that package should stop because it is no longer in the manifests.

Validation

• npm test — 20 tests passed locally.
• npm run lint — Biome passed locally.
• git diff --check origin/main -- . passed locally.
• Final branch diff has no skills/qa/** changes versus origin/main.
• Commit history and PR body contain no QA rewrite work.
• Non-QA reference scan has no remaining /browser, /verify, skills/browser, skills/verify, or agent-browser references.