v0.31.1: admin Users tab + header UX polish

Visual-only patch atop v0.31.0. CSS plus markup/structure in Admin.jsx;
no API, schema, config, overlay, or secret change — a plain frontend
rebuild applies it.

Two latent CSS defects fixed:
- .invite-badge had no rule, so "(pending invite)" rendered as bare
  parenthetical text; it's now a quiet amber pill.
- .btn-link-quiet never reset native <button> chrome, so the admin
  Revoke/Grant/Remove buttons, the modal close ×, and Login/BetaPending
  link-buttons kept the browser's grey button box. The reset the
  .otc-login scope already carried is folded into the base rule.

Users tab: table headers no longer wrap (WRITE-MUTED), timestamps
render as a date-over-time stack, the duplicated subline email is
de-duped, the Create-user-+-invite action moves flush-right beside the
title, and intro DB-column refs read as quiet chips.

Header: the Inbox (§15.2) trigger was styled for a light surface
(gray-200 border, gray-50 hover) and rendered as a pale box that went
white-on-white on hover; restyled to the nav-link vocabulary
(borderless, gray-300 icon → white on a faint translucent hover).

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

frontend/src/components/Admin.jsx

@@ -181,7 +181,20 @@ function UsersTab() {
   return (
     <div className="admin-tab">
       <header className="admin-tab-header">
-        <h2>Users</h2>
+        <div className="admin-tab-heading">
+          <h2>Users</h2>
+          {/* v0.17.0 — roadmap item #16. The "Create user + invite"
+              affordance opens a modal that provisions a fresh users row
+              with the chosen role and sends an invite email with a
+              single-use claim link. */}
+          <div className="admin-tab-actions">
+            <button
+              type="button"
+              className="btn-primary"
+              onClick={() => setInviteModalOpen(true)}
+            >Create user + invite</button>
+          </div>
+        </div>
         <p className="muted">
           The pending bucket is the beta-access review queue (§6.1 /
           v0.8.0). Grant or revoke writes to <code>permission_events</code>
@@ -190,17 +203,6 @@ function UsersTab() {
           retain their v0.7.0 semantics — promote to admin to remove a
           user's ability to write without silencing them.
         </p>
-        {/* v0.17.0 — roadmap item #16. The "Create user + invite"
-            affordance opens a modal that provisions a fresh users row
-            with the chosen role and sends an invite email with a
-            single-use claim link. */}
-        <div className="admin-tab-actions">
-          <button
-            type="button"
-            className="btn-primary"
-            onClick={() => setInviteModalOpen(true)}
-          >Create user + invite</button>
-        </div>
       </header>
       {error && <p className="settings-note warning">{error}</p>}
       {inviteModalOpen && (
@@ -270,21 +272,27 @@ function UserRow({ user: u, busy, onChangeRole, onToggleMute, onFlipPermission }
   // the admin sees at a glance which rows are real users vs. unclaimed
   // invites.
   const pendingInvite = u.pending_invite
+  // When there's no gitea_login the handle already IS the email, so the
+  // subline would otherwise repeat it. Only append the email when it adds
+  // something the handle doesn't already show.
+  const showEmail = u.email && u.email !== handle
   return (
     <>
       <tr>
         <td>
           <div className="user-cell">
-            <span className="user-handle">{handle}</span>
-            {pendingInvite && (
-              <span
-                className="invite-badge"
-                title={`Admin-created invite; expires ${pendingInvite.expires_at}`}
-              >(pending invite)</span>
-            )}
+            <div className="user-cell-handle">
+              <span className="user-handle">{handle}</span>
+              {pendingInvite && (
+                <span
+                  className="invite-badge"
+                  title={`Admin-created invite; expires ${pendingInvite.expires_at}`}
+                >pending invite</span>
+              )}
+            </div>
             <span className="muted">
               {fullName || u.display_name}
-              {u.email ? ` · ${u.email}` : ''}
+              {showEmail ? ` · ${u.email}` : ''}
             </span>
           </div>
         </td>
@@ -317,8 +325,8 @@ function UserRow({ user: u, busy, onChangeRole, onToggleMute, onFlipPermission }
             <span className="muted">N/A</span>
           )}
         </td>
-        <td className="muted">{u.created_at || '—'}</td>
-        <td className="muted">{u.last_seen_at || '—'}</td>
+        <TimeCell value={u.created_at} />
+        <TimeCell value={u.last_seen_at} />
       </tr>
       {state === 'pending' && u.beta_request_reason ? (
         <tr className="user-row-reason">
@@ -334,6 +342,21 @@ function UserRow({ user: u, busy, onChangeRole, onToggleMute, onFlipPermission }
   )
 }
 
+// Render a "YYYY-MM-DD HH:MM:SS" timestamp as an intentional date-over-time
+// stack (date prominent, time quiet below) rather than letting a narrow
+// column wrap the value mid-string. Falls back to an em-dash when absent.
+function TimeCell({ value }) {
+  if (!value) return <td className="muted">—</td>
+  const [date, ...rest] = String(value).split(' ')
+  const time = rest.join(' ')
+  return (
+    <td className="user-when">
+      <span className="user-when-date">{date}</span>
+      {time && <span className="user-when-time muted">{time}</span>}
+    </td>
+  )
+}
+
 function PermissionCell({ user: u, busy, onFlipPermission }) {
   const state = u.permission_state || 'granted'
   const decidedSuffix = u.permission_decided_at