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/app.py

@@ -1,6 +1,7 @@
 """TieMeasureFlow Client - Flask Entry Point."""
 import json
 import os
+from datetime import date
 from urllib.parse import urlparse
 
 from flask import Flask, redirect, url_for, session, request
@@ -101,6 +102,7 @@ def create_app() -> Flask:
             "languages": Config.LANGUAGES,
             "company_logo": session.get("company_logo"),
             "auto_logout_minutes": session.get("auto_logout_minutes"),
+            "current_year": date.today().year,
         }
 
     return app