Implement web session/token revocation (#30)

Web sessions were stateless JWTs with no server-side store: the revocation
hooks in session.service were stubs that only logged. As a result web logout
was client-side only (a copied cookie stayed valid until natural JWT expiry)
and a password change never invalidated existing sessions. The mobile bearer
flow already had revocable, DB-stored tokens; this brings the web/cookie flow
to parity.

Two-layer revocation, both enforced in requireAuth (which already loads the
fresh user row each request):

- Per-session denylist: new `revoked_sessions` table keyed on the JWT `jti`
  (already minted per session). A single logout adds this session's jti;
  rows self-expire at the token's own exp and are pruned on boot. New model
  `revokedSessions` mirrors the `mobileSessions` db/model split.
- Per-user cutoff: new `users.tokens_valid_after` column. A password change
  (and the new `invalidateSessions` helper) bumps it to NOW(); any token whose
  iat is at or before the cutoff is rejected. The comparison is inclusive so a
  token minted in the same wall-clock second as the change is still revoked.

Wiring:
- session.service: revokeSession / invalidateSession / invalidateAllUserSessions
  now delegate to the stores; sessions carry `expiresAt` (JWT exp) so logout can
  set a self-pruning denylist row.
- /logout gains best-effort attachSession so the controller can revoke this
  session's jti and log auth.logout; stays a no-op for anonymous callers.
- users.model.update bumps the cutoff whenever the password hash is rotated.
- schema.sql: revoked_sessions table + tokens_valid_after column, added to the
  CREATE and to the idempotent migration block (ensureSchema on boot).

Verified end-to-end against the local dev DB: a captured cookie is rejected
after logout, and an existing session is rejected after a password change while
re-login with the new password succeeds. Full server test suite green (96).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019rao86n5cXpwAyjdBFEshV

server/src/model/revokedSessions/revokedSessions.db.js

@@ -0,0 +1,40 @@
+const { query } = require('../../utils/db')
+
+// SQL for the revoked_sessions denylist. Rows are keyed on a session's JWT `jti`
+// and carry the token's own expiry so they can be pruned once the underlying JWT
+// would fail verification anyway. This is the web/cookie analogue of
+// mobile_refresh_tokens (opaque, DB-stored, revocable).
+
+// Add a jti to the denylist. INSERT IGNORE makes a repeat logout of the same
+// session a harmless no-op (the PK already exists). Returns rows changed.
+async function add({ jti, userId = null, expiresAt }) {
+  const res = await query(
+    `INSERT IGNORE INTO revoked_sessions (jti, user_id, expires_at)
+     VALUES (?, ?, ?)`,
+    [jti, userId, new Date(expiresAt)],
+  )
+  return Number(res.affectedRows || 0)
+}
+
+// True if this jti is on the denylist and not yet past its stored expiry. Past
+// expiry the token itself is already invalid, so a lingering row need not match.
+async function isRevoked(jti) {
+  if (!jti) return false
+  const rows = await query(
+    'SELECT 1 FROM revoked_sessions WHERE jti = ? AND expires_at > NOW() LIMIT 1',
+    [jti],
+  )
+  return rows.length > 0
+}
+
+// Housekeeping: drop rows whose token has already expired. Returns rows removed.
+async function pruneExpired() {
+  const res = await query('DELETE FROM revoked_sessions WHERE expires_at < NOW()')
+  return Number(res.affectedRows || 0)
+}
+
+module.exports = {
+  add,
+  isRevoked,
+  pruneExpired,
+}

server/src/model/revokedSessions/revokedSessions.model.js

@@ -0,0 +1,29 @@
+// Web/cookie session denylist. Thin logic layer over revokedSessions.db — mirrors
+// the users/mobileSessions split (.db = SQL, .model = the API the rest of the app
+// calls). A "revoked session" is a single JWT jti added on logout; requireAuth
+// checks isRevoked on every authenticated request. Broad invalidation
+// ("everywhere" / password change) does NOT live here — it bumps
+// users.tokens_valid_after instead.
+
+const db = require('./revokedSessions.db')
+
+// Add a session's jti to the denylist (single-session logout). Idempotent.
+async function revoke({ jti, userId, expiresAt }) {
+  return db.add({ jti, userId, expiresAt })
+}
+
+// True if the given jti has been revoked (and its token hasn't expired yet).
+async function isRevoked(jti) {
+  return db.isRevoked(jti)
+}
+
+// Drop denylist rows whose token has already expired.
+async function pruneExpired() {
+  return db.pruneExpired()
+}
+
+module.exports = {
+  revoke,
+  isRevoked,
+  pruneExpired,
+}