feat(auth): unique, changeable, verifiable email addresses (engagement Phase 1b)

Makes `users.email` unique, de-duplicates the addresses an upgrade will find,
and builds the self-service change-and-verify flow that did not exist.

The uniqueness index is on a generated `email_norm AS (LOWER(email)) STORED`
column under `utf8mb4_bin`, NOT on `email` under a `_ci` collation as the plan
specified. Every case-insensitive collation this server offers is also
accent-insensitive: `josé@x.com` and `jose@x.com` compare equal, and those are
two different mailboxes. The plan's index would have refused the second address
forever and the de-duplication would have nulled a legitimate account's.

A requested address is STAGED in `email_pending` and only a tokened link
installs it, so a typo cannot silently redirect account-recovery mail.

`isDuplicateUsername()` now distinguishes the two indexes. All five call sites
branch on it; each answers differently on purpose, because a public form, an
IdP callback, a half-completed invite and an admin screen do not owe the same
person the same amount of truth.

SSO reads the IdP's actual `email_verified`/`verified` claim instead of
inferring verification from an address merely being present.

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

client/src/components/security/EmailAddressPanel.jsx

@@ -0,0 +1,175 @@
+import { useState } from 'react'
+import { api } from '../../api/client.js'
+
+// Self-service email address (engagement Phase 1b). Shared by the player portal
+// and the admin account screen, the same way TrustedDevicesPanel and
+// RecoveryCodesPanel are — /auth/me/account is one surface for every role, so its
+// UI is one component too.
+//
+// The property this component exists to make visible: a requested address is
+// STAGED, not applied. The account keeps receiving mail — password resets
+// included — at the address it already has until the emailed link is opened. If
+// the UI let a pending address look like the address in force, someone who
+// mistyped would believe the change took and would only discover otherwise when
+// they could not recover their account.
+//
+// `hasPassword` decides whether the current-password field appears: an address is
+// where account recovery lands, so changing it is re-authenticated, with the same
+// carve-out the password form makes for an SSO-only account.
+export default function EmailAddressPanel({ account, reload, embedded = false }) {
+  const hasPassword = account.has_password !== false
+  const [email, setEmail] = useState('')
+  const [current, setCurrent] = useState('')
+  const [busy, setBusy] = useState(false)
+  const [msg, setMsg] = useState('')
+  const [error, setError] = useState('')
+
+  const pending = account.email_pending
+
+  async function save(e) {
+    e.preventDefault()
+    setMsg('')
+    setError('')
+    setBusy(true)
+    try {
+      const res = await api.changeEmail(email.trim(), hasPassword ? current : undefined)
+      setEmail('')
+      setCurrent('')
+      // Report an unsent mail honestly. Saying "check your inbox" about a message
+      // that was never sent turns a configuration problem into a user who waits.
+      if (res.emailed === false) {
+        setMsg(
+          res.reason === 'NOT_CONFIGURED'
+            ? 'Address saved, but this site cannot send email right now. Ask an administrator, then use Resend.'
+            : 'Address saved, but the confirmation email could not be sent. Try Resend in a moment.',
+        )
+      } else {
+        setMsg(
+          `Confirmation sent to ${res.email_pending}. Your current address stays in use until you open that link.`,
+        )
+      }
+      await reload()
+    } catch (err) {
+      if (err.status === 429) setError('Too many confirmation emails. Try again later.')
+      else setError(err.message || 'Could not change your email address.')
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  async function resend() {
+    setMsg('')
+    setError('')
+    setBusy(true)
+    try {
+      const res = await api.resendEmailVerification()
+      setMsg(
+        res.emailed === false
+          ? 'Could not send the confirmation email.'
+          : `Confirmation re-sent to ${res.email_pending}.`,
+      )
+    } catch (err) {
+      setError(err.message || 'Could not resend the confirmation email.')
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  async function discard() {
+    setMsg('')
+    setError('')
+    setBusy(true)
+    try {
+      await api.cancelEmailChange()
+      setMsg('Pending address discarded.')
+      await reload()
+    } catch (err) {
+      setError(err.message || 'Could not discard the pending address.')
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  const wrap = embedded
+    ? {}
+    : { marginTop: 40, borderTop: '1px solid var(--line-soft)', paddingTop: 28 }
+
+  return (
+    <div style={wrap}>
+      <h2 className="display" style={{ marginTop: 0, fontSize: '1.2rem', color: 'var(--head)' }}>
+        Email address
+      </h2>
+      <p className="sans" style={{ color: 'var(--muted)', fontSize: '0.9rem', lineHeight: 1.6 }}>
+        {account.email ? (
+          <>
+            Currently <strong style={{ color: 'var(--head)' }}>{account.email}</strong>
+            {account.email_verified ? ' (confirmed)' : ' (not yet confirmed)'}. This is where password-reset
+            email is sent.
+          </>
+        ) : (
+          'You have no email address on file, so you cannot reset your password by email.'
+        )}
+      </p>
+
+      {pending && (
+        <div
+          className="sans"
+          style={{
+            border: '1px solid var(--line-soft)',
+            borderRadius: 6,
+            padding: '10px 12px',
+            marginBottom: 16,
+            fontSize: '0.85rem',
+            color: 'var(--muted)',
+          }}
+        >
+          <strong style={{ color: 'var(--head)' }}>{pending}</strong> is waiting to be confirmed. It is not in
+          use until you open the link in that email.
+          <div style={{ display: 'flex', gap: 8, marginTop: 10 }}>
+            <button type="button" onClick={resend} disabled={busy} className="btn btn-sq">
+              Resend
+            </button>
+            <button type="button" onClick={discard} disabled={busy} className="btn btn-sq">
+              Discard
+            </button>
+          </div>
+        </div>
+      )}
+
+      <form onSubmit={save} style={{ display: 'flex', flexDirection: 'column', gap: 12, maxWidth: 320 }}>
+        <label>
+          <span className="field-label">{pending ? 'Use a different address' : 'New email address'}</span>
+          <input
+            type="email"
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+            className="input"
+            autoComplete="email"
+          />
+        </label>
+        {hasPassword && (
+          <label>
+            <span className="field-label">Current password</span>
+            <input
+              type="password"
+              value={current}
+              onChange={(e) => setCurrent(e.target.value)}
+              className="input"
+              autoComplete="current-password"
+            />
+          </label>
+        )}
+        <div>
+          <button type="submit" disabled={busy || !email.trim()} className="btn btn-primary btn-sq">
+            {busy ? 'Saving…' : 'Send confirmation'}
+          </button>
+        </div>
+        {(msg || error) && (
+          <p className="sans" style={{ margin: 0, fontSize: '0.85rem', color: error ? '#e08a8a' : 'var(--muted)' }}>
+            {error || msg}
+          </p>
+        )}
+      </form>
+    </div>
+  )
+}