Bring player portal in line with Admin + stat-tile My Characters

Implements the "Frontend Theme Redo" design (decision 1a): the logged-in
player portal now uses the same sidebar shell as Admin, and Admin's own
My Characters view gets the same stat-tile treatment.

- PlayerPortalLayout: replace the light 820px top-tab header with the
  Admin sidebar shell (icon nav, sticky content header with page title,
  signed-in footer with sign out). Reuses .admin-grid so the two
  logged-in experiences read as one app.
- Drop the now-redundant inner <h1> from PlayerCharacters/PlayerAccount;
  the title lives in the sticky header.
- CharacterStats: new stat-tile row (Characters / Online now / Linked
  account) that tolerates a restarting shard and hides until an account
  is linked.
- AdminCharacters: render CharacterStats above the roster instead of the
  bare intro paragraph, matching the Player Portal Characters page.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011qPmpmVH1xGCiZoz9m9vW3

client/src/routes/player/PlayerAccount.jsx

@@ -335,7 +335,6 @@ export default function PlayerAccount() {
 
   return (
     <div>
-      <h1 className="display" style={{ margin: '0 0 4px', fontSize: '1.6rem', color: 'var(--head)' }}>Account</h1>
       {loading && <Loading />}
       {error && <ErrorState message={error} />}
       {!loading && !error && account && (