feat(ui,roundtrip): modern neutral “Apple Glass” UI, scenic round trips, and isochrone guidance

- UI (neutral minimal, glass-like)
  - Rewrote app shell and control panel in [app/web/static/index.html](cci:7://file:///home/pedan/freemoto/app/web/static/index.html:0:0-0:0)
  - Modernized responsive styles in [app/web/static/styles.css](cci:7://file:///home/pedan/freemoto/app/web/static/styles.css:0:0-0:0)
  - Proper internal scrolling for control panel, suggestions, waypoints, and directions sheet
  - Improved dark mode, spacing, and visual polish

- Round Trip generation
  - Direction preference (N/E/S/W) with biased waypoint bearings ([route.js](cci:7://file:///home/pedan/freemoto/app/web/static/route.js:0:0-0:0))
  - Ferry avoidance by default on round trips; added strong ferry cost
  - Coastal safety: reverse-geocode water check and automatic inland adjustment for generated waypoints
  - New “Scenic optimizer” option: generate candidate loops, route them, score twistiness, pick the best
    - Heading-change/turn-density based scoring using decoded polyline

- Isochrone-guided loops
  - Backend: added `/isochrone` proxy in [app/web/main.go](cci:7://file:///home/pedan/freemoto/app/web/main.go:0:0-0:0) (derives Valhalla base from `VALHALLA_URL`)
  - Frontend: optional “Use isochrone guidance” + time (minutes); sample preferred sector of polygon

- Settings persistence and live updates
  - Direction, scenic, isochrone, and distance persist via localStorage
  - Changing options regenerates round trips when enabled

- Docker/Build
  - Confirmed multi-arch build (amd64/arm64) and push to git.ztsw.de/pedan/freemoto/freemoto-web:latest

Refs: [index.html](cci:7://file:///home/pedan/freemoto/app/web/static/index.html:0:0-0:0), [styles.css](cci:7://file:///home/pedan/freemoto/app/web/static/styles.css:0:0-0:0), [route.js](cci:7://file:///home/pedan/freemoto/app/web/static/route.js:0:0-0:0), [main.js](cci:7://file:///home/pedan/freemoto/app/web/static/main.js:0:0-0:0), [app/web/main.go](cci:7://file:///home/pedan/freemoto/app/web/main.go:0:0-0:0), [Dockerfile](cci:7://file:///home/pedan/freemoto/Dockerfile:0:0-0:0)

app/web/static/styles.css

@@ -14,13 +14,10 @@
   --shadow-2: 0 10px 30px rgba(2, 8, 20, 0.12);
 }
 
-html, body {
-  height: 100%;
-}
-
+html, body { height: 100%; }
 body {
   margin: 0;
-  overflow: hidden;
+  overflow: hidden; /* map-focused app; internal sections handle their own scroll */
   background: linear-gradient(180deg, #f1f5f9, #e2e8f0);
   color: #0f172a;
 }
@@ -66,6 +63,8 @@ body {
   box-shadow: var(--shadow-2);
   padding: 10px 12px;
   transition: max-height 200ms ease, transform 200ms ease, padding 200ms ease;
+  overflow: auto; /* allow scroll when content grows */
+  max-height: 60vh; /* default for mobile */
 }
 .nav-panel .form-control,
 .nav-panel .btn {
@@ -106,7 +105,7 @@ body {
 .sheet-card {
   border-radius: var(--panel-radius) var(--panel-radius) 0 0;
   max-height: 60vh;
-  overflow: hidden;
+  overflow: hidden; /* header fixed; body scrolls */
   box-shadow: var(--shadow-2);
 }
 .sheet .handle {
@@ -124,10 +123,7 @@ body {
   padding: 4px 8px;
   border-bottom: 1px solid #eef2f6;
 }
-.sheet-body {
-  overflow: auto;
-  max-height: calc(60vh - 42px);
-}
+.sheet-body { overflow: auto; max-height: calc(60vh - 42px); }
 #directionsSheet { display: none; }
 .sheet.collapsed .sheet-card { max-height: 28vh; }
 .sheet.collapsed .sheet-body { max-height: calc(28vh - 42px); }
@@ -172,8 +168,8 @@ body {
     left: 8px;
     right: 8px;
     bottom: 8px;
-    max-height: 48vh;
-    overflow: visible; /* allow suggestion dropdowns to overflow */
+    max-height: 56vh; /* slightly taller for more controls */
+    overflow: auto; /* scroll internally */
   }
   .nav-panel.collapsed {
     max-height: 56px; /* show a small header */
@@ -185,16 +181,18 @@ body {
   .section-title { font-size: 0.95rem; }
 }
 
-/* Desktop layout refinements */
+/* Desktop/tablet layout refinements */
 @media (min-width: 768px) {
   .nav-panel {
     top: 88px;
-    bottom: auto;
+    bottom: 24px; /* allow taller panel while preserving map footer space */
     left: 24px;
     right: auto;
-    width: 560px;
+    width: min(560px, 42vw);
     border-radius: var(--panel-radius);
     padding: 16px;
+    max-height: calc(100vh - 88px - 24px);
+    overflow: auto; /* scroll the panel content when needed */
   }
   .nav-panel .form-control,
   .nav-panel .btn {
@@ -205,6 +203,18 @@ body {
   }
 }
 
+/* Make long lists scrollable inside the panel */
+.nav-panel .list-group {
+  max-height: 34vh;
+  overflow: auto;
+}
+
+/* Scrollbar styling for WebKit browsers */
+*::-webkit-scrollbar { width: 10px; height: 10px; }
+*::-webkit-scrollbar-thumb { background-color: rgba(100, 116, 139, 0.5); border-radius: 8px; }
+*::-webkit-scrollbar-thumb:hover { background-color: rgba(71, 85, 105, 0.7); }
+*::-webkit-scrollbar-track { background: transparent; }
+
 /* Dark theme */
 /* Improved dark mode for readability */
 [data-theme="dark"] :root {