relay UI overhaul, favicon, settings, admin last-seen, fixes

Relay:
  - Inbox/shared/sent split into own view-inbox (nav button + poll).
    Compose is now single-column, centered.
  - Header logo links to compose. Inbox badge stays fresh on all
    views via a quiet loadInbox on every view switch.
  - Mobile menu: full-height sheet below header, larger buttons
    (15px font, 14px padding), full width.
  - Login form wrapped in <form> with name attributes + for/id on
    labels so password managers can autofill.
  - Admin user list shows "last seen <relative time>" per user.
    last_seen_at column on tenants, updated on every authenticated
    request (session + client API).
  - Cache-busting on style.css + app.js via filemtime.
  - View persistence in localStorage (survives reload).
  - Shared-bucket cards show title only (preview line removed).

Favicon:
  - favicon.svg added to project root + copied to public/, relay/,
    website/. Linked via <link rel="icon" type="image/svg+xml"> in
    all three <head> sections.

Settings:
  - New toggle: "Show shopping list items in task collector"
    (default off). collectTasks skips #einkauf/#shopping cards when
    disabled.

Fixes:
  - card-spinner gets display:inline-block so it rotates outside
    flex containers (shopping save spinner).
  - Tim tab test opens the plugin before checking active state.
  - Compose view centered with margin:auto on desktop.

Bumps to 1.9.29.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

relay/inc/auth.php

@@ -24,7 +24,9 @@ function getSessionTenant(PDO $db): ?array {
     if (!$token) return null;
     $stmt = $db->prepare("SELECT t.* FROM sessions s JOIN tenants t ON t.id = s.tenant_id WHERE s.id = :tok AND s.expires_at > datetime('now')");
     $stmt->execute(['tok' => $token]);
-    return $stmt->fetch() ?: null;
+    $tenant = $stmt->fetch() ?: null;
+    if ($tenant) touchLastSeen($db, (int)$tenant['id']);
+    return $tenant;
 }
 
 function destroySession(PDO $db): void {
@@ -62,5 +64,11 @@ function authClient(PDO $db): ?array {
     $tenant = getTenantByUsername($db, $username);
     if (!$tenant) return null;
     if (!password_verify($key, $tenant['secret_hash'])) return null;
+    touchLastSeen($db, (int)$tenant['id']);
     return $tenant;
 }
+
+function touchLastSeen(PDO $db, int $tenantId): void {
+    $db->prepare("UPDATE tenants SET last_seen_at = datetime('now') WHERE id = :id")
+        ->execute(['id' => $tenantId]);
+}