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>

client/src/components/security/TrustLimitModal.jsx

@@ -0,0 +1,124 @@
+import { useState } from 'react'
+import { api } from '../../api/client.js'
+
+// Shown when a user tries to trust a device but is already at the trusted-device
+// cap. Styled like the TOTP entry flow (centered card on a dim overlay). The user
+// MUST revoke at least one existing device before they can continue — there is no
+// silent pruning — or they can cancel and leave the device untrusted.
+//
+// Props:
+//   devices    — the existing trusted devices (from the 409 / trustLimitReached payload)
+//   onTrusted  — called after the current device is successfully trusted (post-revoke)
+//   onCancel   — called when the user backs out without trusting this device
+export default function TrustLimitModal({ devices: initialDevices, onTrusted, onCancel }) {
+  const [devices, setDevices] = useState(initialDevices || [])
+  const [revokedAny, setRevokedAny] = useState(false)
+  const [busy, setBusy] = useState(false)
+  const [error, setError] = useState('')
+
+  async function revoke(id) {
+    setBusy(true)
+    setError('')
+    try {
+      await api.revokeTrustedDevice(id)
+      setDevices((list) => list.filter((d) => d.id !== id))
+      setRevokedAny(true)
+    } catch {
+      setError('Could not revoke that device. Please try again.')
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  async function trustNow() {
+    setBusy(true)
+    setError('')
+    try {
+      await api.trustThisDevice()
+      onTrusted?.()
+    } catch (err) {
+      // Still at the cap somehow (a race) — surface it and let them revoke more.
+      if (err.status === 409 && err.body?.devices) {
+        setDevices(err.body.devices)
+        setError('Still at the limit — revoke another device.')
+      } else {
+        setError('Could not trust this device. Please try again.')
+      }
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  return (
+    <div style={overlay} role="dialog" aria-modal="true" aria-label="Trusted-device limit reached">
+      <div style={card}>
+        <h2 className="display" style={{ margin: '0 0 8px', fontSize: '1.15rem', color: 'var(--head)' }}>
+          Trusted-device limit reached
+        </h2>
+        <p className="sans" style={{ margin: '0 0 16px', color: 'var(--muted)', fontSize: '0.88rem', lineHeight: 1.6 }}>
+          You can trust up to {Math.max(devices.length, 1)} devices. Revoke one below to make room, then
+          continue — or cancel to leave this device untrusted.
+        </p>
+
+        <div style={{ display: 'flex', flexDirection: 'column', gap: 8, marginBottom: 16, maxHeight: 240, overflowY: 'auto' }}>
+          {devices.map((d) => (
+            <div key={d.id} style={row}>
+              <div style={{ flex: 1, minWidth: 0 }}>
+                <div className="sans" style={{ color: 'var(--head)', fontSize: '0.88rem' }}>
+                  {d.deviceName || d.platform || 'Device'}
+                </div>
+                <div className="sans dim" style={{ fontSize: '0.74rem', overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>
+                  {d.userAgent || '—'}
+                </div>
+              </div>
+              <button onClick={() => revoke(d.id)} disabled={busy} className="pill" style={{ color: '#d98b84', borderColor: '#d98b84' }}>
+                Revoke
+              </button>
+            </div>
+          ))}
+          {devices.length === 0 && (
+            <p className="sans dim" style={{ fontSize: '0.84rem', margin: 0 }}>All devices revoked. You can trust this one now.</p>
+          )}
+        </div>
+
+        {error && <p className="sans" style={{ margin: '0 0 12px', color: '#d98b84', fontSize: '0.84rem' }}>{error}</p>}
+
+        <div style={{ display: 'flex', gap: 10, alignItems: 'center' }}>
+          <button onClick={trustNow} disabled={busy || !revokedAny} className="btn btn-primary btn-sq">
+            {busy ? 'Working…' : 'Trust this device'}
+          </button>
+          <button onClick={onCancel} disabled={busy} className="pill">
+            Cancel
+          </button>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+const overlay = {
+  position: 'fixed',
+  inset: 0,
+  background: 'rgba(0,0,0,0.6)',
+  display: 'flex',
+  alignItems: 'center',
+  justifyContent: 'center',
+  padding: 16,
+  zIndex: 1000,
+}
+const card = {
+  width: '100%',
+  maxWidth: 460,
+  background: 'var(--panel, #1a1a1f)',
+  border: '1px solid var(--line)',
+  borderRadius: 12,
+  padding: 24,
+}
+const row = {
+  display: 'flex',
+  alignItems: 'center',
+  gap: 12,
+  padding: '10px 14px',
+  border: '1px solid var(--line)',
+  borderRadius: 8,
+}