Add PWA native feel: manifest, meta tags, install prompt, SW optimization, dynamic theme-color

Configure manifest.json with scope, maskable icons, and categories. Add iOS/Android
meta tags for standalone behavior. Create pwa.css for native touch/scroll handling
and safe area insets. Add oikos-install-prompt Web Component with Chrome install
flow and iOS guidance. Optimize service worker with network-first navigation and
expanded precache (v19). Add dynamic theme-color per route and modal overlay dimming
in standalone mode. Generate placeholder icons via sharp script.

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

public/styles/pwa.css

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+/**
+ * Modul: PWA Native Feel
+ * Zweck: Natives Touch- und Scrollverhalten, Safe Areas, Touch-Targets
+ * Abhängigkeiten: tokens.css, layout.css
+ */
+
+/* ── Kein Rubber-Banding / Pull-to-Refresh des Browsers ── */
+html, body {
+  overscroll-behavior: none;
+}
+
+/* ── Kein Tap-Highlight auf allen Elementen (Android Chrome) ──
+ * reset.css setzt es nur auf html; hier global für alle Elemente */
+* {
+  -webkit-tap-highlight-color: transparent;
+}
+
+/* ── Safe Area Insets (Notch, Dynamic Island, Gesture Bar) ── */
+body {
+  padding-top: env(safe-area-inset-top);
+  padding-bottom: env(safe-area-inset-bottom);
+  padding-left: env(safe-area-inset-left);
+  padding-right: env(safe-area-inset-right);
+}
+
+/* ── Bottom Nav über der Gesture Bar ──
+ * layout.css nutzt --safe-area-inset-bottom Token;
+ * hier als Fallback direkt via env() */
+.nav-bottom {
+  padding-bottom: env(safe-area-inset-bottom);
+}
+
+/* ── Touch-Targets: min 44×44px (Apple HIG / WCAG 2.5.5) ── */
+button, a, [role="button"], input[type="checkbox"], input[type="radio"] {
+  min-height: 44px;
+  min-width: 44px;
+}
+
+/* ── Smooth Momentum-Scrolling in scrollbaren Containern ── */
+.scroll-container,
+.nav-bottom__scroll {
+  overflow-y: auto;
+  -webkit-overflow-scrolling: touch;
+  overscroll-behavior-y: contain;
+}
+
+/* ── Kein Text-Selection in UI-Elementen (nur in Content-Bereichen) ── */
+nav,
+.nav-bottom,
+.nav-sidebar,
+.cal-toolbar,
+.tasks-toolbar,
+.notes-toolbar,
+.contacts-toolbar,
+.modal-panel__header {
+  -webkit-user-select: none;
+  user-select: none;
+}
+
+/* ── Standalone-Modus: Status-Bar-Bereich berücksichtigen ── */
+@media (display-mode: standalone) {
+  body {
+    padding-top: env(safe-area-inset-top);
+  }
+}