Add session abstraction, mobile bearer auth, and pluggable SSO

Refactor authentication into a provider-agnostic session layer and build
two new auth surfaces on top of it, without changing local password/TOTP
behavior. Every flow now issues sessions through
sessionService.createSession(user, authMethod).

Part 1 — Session abstraction (backward-compatible refactor):
- New server/src/auth/: token.js (JWT/cookie primitives), session.service.js
  (create/validate/partial-TOTP/revoke), session.middleware.js
  (attachSession/requireAuth/requireRole). utils/auth.js is now a thin
  compat facade so existing imports are unchanged.

Part 2 — Mobile bearer auth (additive):
- /api/v1/auth/mobile/{login,refresh,logout}: short-lived access JWT +
  long-lived refresh token, stored hashed and rotated on use, in a new
  mobile_refresh_tokens table. Reuses web bot-scoring/backoff; single-request
  TOTP. token.signToken gains a backward-compatible expiresIn option.

Part 3 — Pluggable SSO (Google, Discord, generic OIDC):
- OAuth2Provider base + built-in Google/Discord (fixed endpoints) + generic
  OIDC, a registry with health/validation, PKCE+CSRF transaction state, and
  discovery (GET /auth/providers), start/link/callback routes.
- Link-only policy: SSO signs in only to an already-linked account; external
  identities are never auto-provisioned. Client secrets encrypted at rest
  (AES-256-GCM, utils/secretBox.js). Admin CRUD (/admin/auth/providers) and
  account linking (/admin/account/identities). New auth_providers +
  user_identities tables.

Frontend:
- Login page renders provider buttons from /auth/providers (inline SVG icons,
  graceful with zero providers). New Authentication admin view
  (Local/Google/Discord/Custom). Account page linked-accounts section.

Tests: 83 passing (session, mobile, providers, registry, secretBox, ssoState,
ssoCallback) — all DB-free via fetch mocks + model stubs. README + .env.example
updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/model/mobileSessions/mobileSessions.db.js

@@ -0,0 +1,62 @@
+const { query } = require('../../utils/db')
+
+// SQL for the mobile_refresh_tokens table. Tokens are stored only as sha256
+// hashes (token_hash); the raw refresh token never touches the database.
+
+// Insert a new refresh-token row. expiresAt is a JS Date (or ms epoch).
+async function insert({ userId, tokenHash, deviceHash = null, userAgent = null, expiresAt }) {
+  const res = await query(
+    `INSERT INTO mobile_refresh_tokens (user_id, token_hash, device_hash, user_agent, expires_at)
+     VALUES (?, ?, ?, ?, ?)`,
+    [userId, tokenHash, deviceHash, userAgent, new Date(expiresAt)],
+  )
+  return res.insertId
+}
+
+// Look up a token by hash only if it is still usable: not revoked and not past
+// its expiry. Returns the row (incl. user_id) or null.
+async function findValidByHash(tokenHash) {
+  const rows = await query(
+    `SELECT * FROM mobile_refresh_tokens
+     WHERE token_hash = ? AND revoked_at IS NULL AND expires_at > NOW()
+     LIMIT 1`,
+    [tokenHash],
+  )
+  return rows[0] || null
+}
+
+// Mark a single token revoked (idempotent — only affects a not-yet-revoked row).
+// Returns the number of rows changed.
+async function revokeByHash(tokenHash) {
+  const res = await query(
+    'UPDATE mobile_refresh_tokens SET revoked_at = NOW() WHERE token_hash = ? AND revoked_at IS NULL',
+    [tokenHash],
+  )
+  return Number(res.affectedRows || 0)
+}
+
+// Revoke every active token for a user (logout-everywhere). Returns rows changed.
+async function revokeAllForUser(userId) {
+  const res = await query(
+    'UPDATE mobile_refresh_tokens SET revoked_at = NOW() WHERE user_id = ? AND revoked_at IS NULL',
+    [userId],
+  )
+  return Number(res.affectedRows || 0)
+}
+
+// Housekeeping: delete rows that are long dead (expired or revoked). Keeps the
+// table from growing without bound. Returns rows removed.
+async function pruneExpired() {
+  const res = await query(
+    'DELETE FROM mobile_refresh_tokens WHERE expires_at < NOW() OR revoked_at IS NOT NULL',
+  )
+  return Number(res.affectedRows || 0)
+}
+
+module.exports = {
+  insert,
+  findValidByHash,
+  revokeByHash,
+  revokeAllForUser,
+  pruneExpired,
+}

server/src/model/mobileSessions/mobileSessions.model.js

@@ -0,0 +1,40 @@
+// Mobile refresh-token store. Thin logic layer over mobileSessions.db — mirrors
+// the users model split (.db = SQL, .model = the API the rest of the app calls).
+// The refresh token itself is opaque and lives client-side; only its hash is
+// persisted (hashing is done by the session service so caller + store agree).
+
+const db = require('./mobileSessions.db')
+
+// Persist a newly issued refresh token (by hash). Returns the row id.
+async function store({ userId, tokenHash, deviceHash, userAgent, expiresAt }) {
+  return db.insert({ userId, tokenHash, deviceHash, userAgent, expiresAt })
+}
+
+// Return the stored row for a still-valid (unrevoked, unexpired) token, else null.
+async function findValidByHash(tokenHash) {
+  return db.findValidByHash(tokenHash)
+}
+
+// Revoke one refresh token (logout / rotation). Returns rows changed (0 if it was
+// already gone/revoked — callers treat this idempotently).
+async function revokeByHash(tokenHash) {
+  return db.revokeByHash(tokenHash)
+}
+
+// Revoke all of a user's refresh tokens (logout everywhere).
+async function revokeAllForUser(userId) {
+  return db.revokeAllForUser(userId)
+}
+
+// Drop expired/revoked rows.
+async function pruneExpired() {
+  return db.pruneExpired()
+}
+
+module.exports = {
+  store,
+  findValidByHash,
+  revokeByHash,
+  revokeAllForUser,
+  pruneExpired,
+}