feat: detect revoked GitHub token and prompt re-authentication

[Subhra-Nandi]

Summary

Closes #884

The JWT callback in auth.ts already validates the stored token every 24h
and sets session.error = "TokenRevoked" when GitHub returns 401. This PR
completes the user-facing side — detecting that flag and redirecting the user
to sign in with a clear message instead of silently showing empty widgets.

Changes

File	Change
src/app/auth/signin/page.tsx	Add TokenRevoked to AUTH_ERROR_MESSAGES
src/components/TokenRevokedGuard.tsx	New — client component, signs out and redirects on revocation
src/app/dashboard/page.tsx	Mount TokenRevokedGuard
package.json	Add missing rehype-sanitize dependency

How It Works

1. User revokes DevTrack access in GitHub Settings → Applications
2. Within 24h the jwt callback hits GET /api.github.com/user → gets 401
3. token.error = "TokenRevoked" is set on the JWT
4. session.error = "TokenRevoked" is surfaced to the client
5. TokenRevokedGuard detects this and calls signOut({ callbackUrl: "/auth/signin?error=TokenRevoked" })
6. Signin page shows: "Your GitHub access was revoked. Please sign in again to continue."

What Was Already There (untouched)

• auth.ts — full token validation logic ✅
• next-auth.d.ts — types for session.error ✅
• error-utils.ts — safe error message string ✅
• wrapped/page.tsx — already handles TokenRevoked ✅

Screenshots

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Priyanshu-byte-coder]

CI is failing because this branch is based on an older version of main that still had @emnapi/core and @emnapi/runtime in the lockfile. Those have since been removed from main.

Please rebase on main:

git fetch origin
git rebase origin/main
git push --force-with-lease