security: internal audit — batch 1

Fixes the critical + high + medium findings from our internal security
review. Bundled into one PR because the changes overlap heavily (JWT
verification unifies across three call sites; backup-code hashing and
demo-email handling cross-cut several services); splitting them out
would mean redundant reviews of the same files.

Critical
- CI-C1 — .github/workflows/test.yml: restore actions/{checkout,setup-
  node,upload-artifact} to @v4. The @v6 refs don't exist, so the test
  workflow was errorring before a single test ran.
- SEC-C1 — mfaPolicy now extracts the token via extractToken() (cookie-
  first, Bearer fallback). Previously it only read Authorization, so
  every cookie-authenticated SPA session bypassed require_mfa entirely.
- SEC-C2/C4/C6 — all JWT verification paths (MCP bearer, file download,
  photo route) now go through the shared verifyJwtAndLoadUser that
  checks password_version. resetPassword additionally deletes every
  mcp_tokens row and marks outstanding oauth_tokens revoked, so a
  password reset invalidates ALL credential classes — not just the
  cookie JWT.

High
- SEC-H2 — reset email URL is built from server-side APP_URL /
  ALLOWED_ORIGINS (via existing getAppUrl()), not request headers.
  Closes the host-header-injection vector into reset links.
- SEC-H3 — OIDC findOrCreateUser wraps the invite-redemption UPDATE +
  user INSERT in a transaction. The UPDATE is the capacity check; if
  a concurrent callback takes the last slot, the whole transaction
  aborts with registration_disabled instead of double-creating users.
- SEC-H4 — new verifyIdToken() performs full JWT signature
  verification via the provider's JWKS (Node's crypto.createPublicKey
  accepts JWK directly — no extra dependency), plus iss/aud/exp
  checks. The callback also rejects the login when userinfo.sub does
  not match id_token.sub.
- SEC-H5 — OAuth DCR now validates redirect_uris against an allowlist
  of schemes: https, http-loopback, or a private custom scheme. Plain
  http://non-loopback is rejected.
- SEC-H6 — oauthService audience defaults to mcpResource when the
  `resource` parameter is missing, so tokens are always audience-bound
  to /mcp instead of being issued with audience=null.
- SEC-H7 — HSTS is enabled any time NODE_ENV=production (previously
  required FORCE_HTTPS=true), includeSubDomains defaults on and can
  be disabled with HSTS_INCLUDE_SUBDOMAINS=false.
- SEC-H8 — trek_session cookie Secure flag is also driven by
  req.secure (which Express resolves from X-Forwarded-Proto once
  trust proxy is set), so instances behind a TLS-terminating proxy
  get Secure cookies without needing FORCE_HTTPS.

Medium
- SEC-M1 — permanentDeleteFile / emptyTrash / avatar unlink now use
  fs.promises.rm with { force: true } (one async op vs the previous
  existsSync + unlinkSync pair per file).
- SEC-M2 — invalidatePermissionsCache() is called inside restoreFromZip
  so a restored DB with different permission rows is honoured
  immediately.
- SEC-M3 + C1 — idempotency store bounds the key at 128 chars, caches
  only responses ≤ 256 KiB, and scopes the lookup by (key, user_id,
  method, path) rather than (key, user_id). Same key replayed against
  a different endpoint no longer returns a stale unrelated body.
- SEC-M4 — share_tokens gets an expires_at column; new tokens default
  to 90-day TTL, expired tokens are denied at lookup. Existing tokens
  stay NULL = no expiry so already-published links don't break.
- SEC-M5 — /uploads/photos/:filename now resolves the photo to its
  trip_id and requires the share token to cover THAT trip. Previously
  any share token for any trip would unlock any photo filename.
- SEC-M6 — BLOCKED_EXTENSIONS is the single source of truth shared
  between fileService and collab uploads. The '*' allowed_file_types
  wildcard now still rejects executables/scripts.
- SEC-M7 — single DEMO_EMAILS constant (services/demo.ts) used by
  demoUploadBlock, mfaPolicy, and every demo-mode guard in
  authService. The old demoUploadBlock only matched 'demo@nomad.app'
  so the seed 'demo@trek.app' could in fact upload in demo mode.
- SEC-M8 — MFA backup codes are now bcrypt-hashed at rest
  (hashBackupCodeBcrypt). matchBackupCode accepts both bcrypt and
  legacy SHA-256 hex hashes, so existing installs keep working until
  the user regenerates codes via enableMfa.
- SEC-M9 — document the "security via UUID v4 filename" model for
  /uploads/avatars|covers|journey. Requires no code change but
  captures the decision so future reviewers don't re-flag it.
- SEC-M10 — already covered by the resetPassword revocation logic
  above: mcp_tokens DELETE + oauth_tokens UPDATE … SET revoked_at.

Performance
- PERF-H1 — new migration adds the indexes flagged in the audit:
  trips(user_id), trips(created_at DESC), photos(day_id),
  photos(place_id), reservations(day_id), share_tokens(token), plus
  conditional day_accommodations and notifications indexes depending
  on which columns are present.

Tests
- tests/integration/oidc.test.ts now mocks verifyIdToken and passes
  an id_token in the exchangeCodeForToken stub for the three flows
  that exercise a successful callback. The three remaining failures
  tests pointed out were all pre-existing (file-upload flakes +
  notificationPreferences event_types count drift), none introduced
  by this PR.

.github/workflows/test.yml

@@ -17,9 +17,9 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v6
+      - uses: actions/setup-node@v4
         with:
           node-version: 22
           cache: npm
@@ -33,7 +33,7 @@ jobs:
 
       - name: Upload coverage
         if: success()
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v4
         with:
           name: backend-coverage
           path: server/coverage/
@@ -44,9 +44,9 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v6
+      - uses: actions/setup-node@v4
         with:
           node-version: 22
           cache: npm
@@ -60,7 +60,7 @@ jobs:
 
       - name: Upload coverage
         if: success()
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v4
         with:
           name: frontend-coverage
           path: client/coverage/