Address seven review findings across detectors, CLI, and CI

[Conalh]

Summary

Implements the seven follow-ups from the review pass. Each is independently testable and lands with a focused regression test.

• Emit GitHub annotations for drift findings #2 range detection — mcp-risk.ts now treats @vendor/pkg@^1.2.3, ~1.2.3, >=1.2.3, *, and bare names as unpinned. The previous looksLikePackageName regex rejected range operators entirely so these slipped past the npx/bunx/uvx/pipx unpinned check.
• Demo: risky agent permission drift #3 parsed TOML — detectCodexConfigDrift walks the parseToml tree for sandbox/approval/network keys, so inline tables like sandbox_workspace_write = { network_access = true } and windows = { sandbox = "danger-full-access" } produce findings instead of rating none. The split between regex parsing (sandbox/approval/network) and parseToml (trusted projects) is gone.
• Add traction plan and feedback intake #4 git-ref errors — git-snapshot.ts exports a ScopeTrailError; verifyGitRef wraps rev-parse failures with a concise message that names the ref and hints at fetch-depth: 0. Caught in main() so the CLI exits 2 with that message instead of leaking a Node stack trace.
• Add public CI and Action metadata #5 Node support — package.json declares engines.node: ">=20" (matching agent-gov-core@>=0.7's requirement), and CI matrices Node 20/22/24.
• Add line-level GitHub annotations #6 hygiene — temp dirs in test/codex-config-drift.test.mjs use os.tmpdir() (the import was already there, unused) instead of writing under node_modules/.
• Update checkout action to v6 #7 --fail-on in CLI — threshold logic moved into src/index.ts via meetsFailOnThreshold in report.ts. action.yml now passes --fail-on $fail_on to the CLI and captures exit status, removing the bash rank table.
• Add GitHub Action diff mode #1 repo cleanup — 74f3f52 already untracked the demo .mcp.json / .claude/settings.json. This PR adds .gitignore rules matching the existing /.codex/ pattern and a regression test in test/package-surface.test.mjs so the live demo files can't come back unnoticed.

Five new tests added; one CI workflow assertion updated for the Node matrix. The action wrapper drops the bash rank helper in favor of the CLI gate.

Test plan

• npm test — 66/66 pass (was 59/59)
• npx tsc -p tsconfig.json --noEmit — exit 0
• npm pack --dry-run --json — 17 packaged files, no change
• npm audit --omit=dev — 0 vulnerabilities
• CI Node 20/22/24 matrix passes on PR
• Confirm scopetrail.yml dogfood run produces a clean advisory report on this PR (no false-positives from the new detector behavior)

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