Add multi-user auth, admin panel, and timezone support; rename to Yolkbook

- Rename app from Eggtracker to Yolkbook throughout
- Add JWT-based authentication (python-jose, passlib/bcrypt)
- Add users table; all data tables gain user_id FK for full data isolation
- Super admin credentials sourced from ADMIN_USERNAME/ADMIN_PASSWORD env vars,
  synced on every startup; orphaned rows auto-assigned to admin post-migration
- Login page with self-registration; JWT stored in localStorage (30-day expiry)
- Admin panel (/admin): list users, reset passwords, disable/enable, delete,
  and impersonate (Login As) with Return to Admin banner
- Settings modal (gear icon in nav): timezone selector and change password
- Timezone stored per-user; stats date windows computed in user's timezone;
  date input setToday() respects user timezone via Intl API
- migrate_v2.sql for existing single-user installs
- Auto-migration adds timezone column to users on startup
- Updated README with full setup, auth, admin, and migration docs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nginx/html/css/style.css

@@ -173,6 +173,7 @@ label { font-size: 0.875rem; font-weight: 500; }
 input[type="text"],
 input[type="number"],
 input[type="date"],
+input[type="password"],
 textarea,
 select {
     padding: 0.5rem 0.75rem;
@@ -259,4 +260,120 @@ td input[type="date"] {
     .nav-links { overflow-x: auto; scrollbar-width: none; }
     .nav-links::-webkit-scrollbar { display: none; }
     .nav-links a { padding: 0.4rem 0.55rem; font-size: 0.82rem; white-space: nowrap; }
+    .nav-username { display: none; }
+}
+
+/* ── Nav user section ─────────────────────────────────────────────────────── */
+.nav-user {
+    margin-left: auto;
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    flex-shrink: 0;
+}
+
+.nav-username {
+    color: rgba(255,255,255,0.85);
+    font-size: 0.88rem;
+    white-space: nowrap;
+}
+
+.nav-impersonating {
+    color: #ffe08a;
+    font-size: 0.85rem;
+    white-space: nowrap;
+}
+
+.nav-admin-btn {
+    color: rgba(255,255,255,0.85) !important;
+    border-color: rgba(255,255,255,0.35) !important;
+}
+.nav-admin-btn:hover {
+    background: rgba(255,255,255,0.15) !important;
+    color: #fff !important;
+}
+
+.btn-amber { background: var(--amber); color: #fff; }
+.btn-amber:hover { background: #b8720a; }
+
+/* ── Login page ───────────────────────────────────────────────────────────── */
+.login-body {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    min-height: 100vh;
+    background: var(--bg);
+}
+
+.login-container {
+    width: 100%;
+    max-width: 380px;
+    padding: 0 1rem;
+}
+
+.login-brand {
+    text-align: center;
+    font-size: 1.6rem;
+    font-weight: 700;
+    color: var(--green);
+    margin-bottom: 1.5rem;
+}
+
+.login-card { padding: 2rem; }
+
+.login-title {
+    text-align: center;
+    font-size: 1.3rem;
+    margin-bottom: 1.25rem;
+}
+
+/* ── Modals ───────────────────────────────────────────────────────────────── */
+.modal-overlay {
+    position: fixed;
+    inset: 0;
+    background: rgba(0,0,0,0.45);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 500;
+    padding: 1rem;
+}
+
+.modal-box {
+    background: var(--card-bg);
+    border-radius: var(--radius);
+    padding: 1.75rem;
+    width: 100%;
+    max-width: 420px;
+    box-shadow: 0 8px 32px rgba(0,0,0,0.18);
+}
+
+.modal-box h2 { margin-bottom: 1rem; }
+
+/* ── Badges ───────────────────────────────────────────────────────────────── */
+.badge {
+    display: inline-block;
+    padding: 0.2rem 0.55rem;
+    border-radius: 99px;
+    font-size: 0.75rem;
+    font-weight: 600;
+}
+
+.badge-admin    { background: #d4edff; color: #0055aa; }
+.badge-user     { background: #e8f5e9; color: #2e6b3e; }
+.badge-active   { background: #d4edda; color: #155724; }
+.badge-disabled { background: #f8d7da; color: #721c24; }
+
+/* ── Settings modal extras ────────────────────────────────────────────────── */
+.settings-section-title {
+    font-size: 0.95rem;
+    font-weight: 600;
+    color: var(--green-dark);
+    margin-bottom: 0.75rem;
+}
+
+.settings-divider {
+    border: none;
+    border-top: 1px solid var(--border);
+    margin: 1.25rem 0;
 }