feat(web): Tailwind-Redesign, Tag/Nacht-Umschalter, Mobile-Fixes

- responsives, modernes Layout mit Tailwind (CDN, kein Build); aufgeraeumter Header
  (einheitliche Groessen/Farben, neutrale Palette, ein Akzent)
- Tag-/Nacht-Umschalter: manuell + folgt automatisch dem System (kein Flackern)
- Mobile: App-Shell h-[100dvh] mit fixem Eingabe-Footer + safe-area-Padding
  -> kein grosser Abstand mehr zum unteren Bildschirmrand
- "Metriken"-Link entfernt (fuer Endnutzer irrelevant); Admin-Nutzerliste als Toggle
- style.css entfernt (komplett Tailwind), Asset-Version v6

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/web/style.css

@@ -1,82 +0,0 @@
-* { box-sizing: border-box; }
-html, body { height: 100%; }
-body {
-  margin: 0;
-  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
-  color: #1c1c1c;
-  background: #f6f7f9;
-}
-/* Echte (dynamische) Viewport-Hoehe: auf iOS beruecksichtigt 100dvh die
-   ein-/ausblendende Browserleiste; 100vh als Fallback fuer aeltere Browser. */
-#layout { display: flex; height: 100vh; height: 100dvh; overflow: hidden; }
-
-#menu {
-  width: 240px;
-  flex-shrink: 0;
-  overflow-y: auto;
-  background: #1f2933;
-  color: #e4e7eb;
-  padding: 1rem;
-  display: flex;
-  flex-direction: column;
-  gap: 1rem;
-}
-#menu h2 { font-size: 1.1rem; margin: 0; }
-#menu h3 { font-size: 0.9rem; margin: 0 0 0.5rem; text-transform: uppercase; letter-spacing: 0.05em; }
-#menu a { color: #9fd3ff; }
-#identity { font-size: 0.9rem; }
-#tts-row { font-size: 0.85rem; display: flex; gap: 0.4rem; align-items: center; }
-#tts { flex: 1; padding: 0.3rem; border-radius: 0.4rem; border: 1px solid #52606d; }
-.muted { color: #7b8794; font-size: 0.85rem; }
-.hidden { display: none; }
-
-#user-list { list-style: none; padding: 0; margin: 0 0 0.5rem; font-size: 0.85rem; }
-#user-list li { padding: 0.15rem 0; border-bottom: 1px solid #323f4b; }
-
-#chat { flex: 1; min-height: 0; display: flex; flex-direction: column; padding: 1rem; max-width: 820px; margin: 0 auto; width: 100%; }
-/* min-height:0 erlaubt dem Flex-Kind zu schrumpfen -> nur DIESER Bereich scrollt. */
-#messages {
-  flex: 1;
-  min-height: 0;
-  overflow-y: auto;
-  -webkit-overflow-scrolling: touch;
-  overscroll-behavior: contain;
-  display: flex;
-  flex-direction: column;
-  gap: 0.6rem;
-  padding-bottom: 0.5rem;
-}
-
-.msg { padding: 0.6rem 0.8rem; border-radius: 0.8rem; max-width: 80%; white-space: pre-wrap; line-height: 1.4; }
-.msg.user { align-self: flex-end; background: #2b6cb0; color: #fff; }
-.msg.assistant { align-self: flex-start; background: #fff; border: 1px solid #e1e4e8; }
-.msg.system { align-self: center; background: #fdf3d7; border: 1px solid #f0d98c; font-size: 0.85rem; }
-.msg.emergency { align-self: center; background: #fde0e0; border: 1px solid #f5a3a3; font-weight: 600; }
-
-/* Eingabe + Mic bleiben immer sichtbar (fester Fuss des Chat-Bereichs). */
-#prompt-form { display: flex; gap: 0.5rem; align-items: center; flex-shrink: 0; padding-top: 0.5rem; }
-#prompt { flex: 1; padding: 0.7rem; border: 1px solid #cbd2d9; border-radius: 0.6rem; font-size: 1rem; }
-button { padding: 0.7rem 1rem; border: none; border-radius: 0.6rem; background: #2b6cb0; color: #fff; font-size: 1rem; cursor: pointer; }
-button:disabled { opacity: 0.5; cursor: default; }
-#mic { background: #2f855a; }
-#mic.recording { background: #c53030; animation: pulse 1s infinite; }
-@keyframes pulse { 0%,100% { opacity: 1; } 50% { opacity: 0.6; } }
-#status { min-height: 1.2rem; margin-top: 0.4rem; flex-shrink: 0; }
-
-@media (max-width: 640px) {
-  #layout { flex-direction: column; }
-  /* Menue als kompakte, nicht scrollende Kopfleiste; der Chat fuellt den Rest. */
-  #menu {
-    width: 100%;
-    flex-shrink: 0;
-    flex-direction: row;
-    flex-wrap: wrap;
-    align-items: center;
-    gap: 0.5rem;
-    padding: 0.6rem 1rem;
-  }
-  #menu h2 { flex: 1; font-size: 1rem; }
-  #menu h3 { display: none; }
-  #admin { width: 100%; order: 3; }
-  #chat { flex: 1; min-height: 0; padding: 0.6rem; }
-}