ui: restyle login, dedupe navbar with Jinja macros, touch polish

- login: theme variables instead of hardcoded slate colors, decorative
  brand background, show/hide password toggle, dynamic copyright year
- navbar: nav links rendered via shared nav_link/nav_links macros
  (desktop + mobile from one source), active state now also in mobile
  menu, aria-current on active link, fix nonexistent w-4.5 class
- themes.css: btn :active press feedback, btn-lg variant, card hover
  border accent, brand accent-color and ::selection
- fix tmf-input vs pl-10 cascade conflict (themes.css loads after
  tailwind.css) with important utilities — also fixes recipe search icon
- app.py: inject current_year in template globals
- i18n: add Mostra/Nascondi password (IT/EN)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/frontend/flask_app/static/css/themes.css

@@ -69,6 +69,23 @@
 }
 
 
+/* ============================================================
+   Brand details
+   ============================================================ */
+
+:root {
+  accent-color: var(--color-primary);
+}
+
+::selection {
+  background: rgba(37, 99, 235, 0.2);
+}
+
+.dark ::selection {
+  background: rgba(96, 165, 250, 0.3);
+}
+
+
 /* ============================================================
    Global Transitions
    ============================================================ */
@@ -151,6 +168,7 @@ textarea:focus-visible {
 
 .tmf-card:hover {
   box-shadow: var(--shadow-md);
+  border-color: var(--scrollbar-thumb);
 }
 
 .tmf-card-header {
@@ -250,11 +268,21 @@ textarea:focus-visible {
   border: 1px solid transparent;
 }
 
+.btn:active:not(:disabled) {
+  transform: scale(0.97);
+}
+
 .btn:disabled {
   opacity: 0.5;
   cursor: not-allowed;
 }
 
+.btn-lg {
+  padding: 0.75rem 1.5rem;
+  font-size: 1rem;
+  border-radius: 0.625rem;
+}
+
 .btn-primary {
   background: var(--color-primary);
   color: #FFFFFF;