feat(auth): trusted devices, recovery codes, and admin MFA management

Add opt-in "Trust this device" so a browser/app skips the TOTP step (never
the password) for 30 days, single-use bcrypt recovery codes as a 2FA-lockout
fallback, and admin trusted-device/MFA-reset management — backend, web UI,
OpenAPI spec, and tests.

- Schema: trusted_devices (sha256 token hash, looked up by unique index) and
  recovery_codes (bcrypt, single-use). Both additive/idempotent.
- Session service: trust-token mint/hash/resolve + cap helpers; new rg_trust
  httpOnly cookie (survives logout, revoked on untrust/password change/reset/
  TOTP disable). JWTs stay stateless — trust is a server-side row, not a claim.
- Web + mobile login accept a trusted-device token / recovery code; login/totp
  gains trustDevice + recoveryCode. Cap of 10/user with NO silent pruning — an
  over-cap trust returns 409/trustLimitReached and the client prompts to revoke.
- Self-service /auth/me/trusted-devices* + recovery-codes*; admin
  /admin/users/:id/trusted-devices* + /mfa/reset. All actions audit-logged.
- Client: "Trust this device" + recovery-code login options, one-time recovery
  code display, Trusted Devices + Recovery Codes account panels, a TOTP-styled
  revoke-to-continue cap modal, and admin per-user security controls.
- OpenAPI regenerated; 33 new server tests (all suites green).

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

server/.env.example

@@ -27,6 +27,15 @@ JWT_EXPIRES_IN=1d
 COOKIE_SECURE=auto
 COOKIE_NAME=rg_token
 
+# Trusted-device MFA ("Trust this device"). The trust cookie's name, how long a
+# device stays trusted (skips the TOTP step, never the password), the per-user cap
+# (no silent pruning — an over-cap trust is refused), and how many single-use
+# recovery codes are generated at 2FA enrollment.
+TRUST_COOKIE_NAME=rg_trust
+TRUSTED_DEVICE_TTL_DAYS=30
+MAX_TRUSTED_DEVICES=10
+RECOVERY_CODE_COUNT=10
+
 # Encryption key for secrets stored at rest (OAuth client secrets in auth_providers).
 # Any string — hashed to a 256-bit AES-GCM key. REQUIRED in production; in dev an
 # insecure key is derived from JWT_SECRET if unset (with a warning).