Add route interactions: click-to-split, drag-to-reshape, colored route rendering

- Enrich BRouter response with per-point 3D coordinates and segment boundary
  tracking (EnrichedRoute interface)
- ColoredRoute component: plain, elevation gradient (green→yellow→red), and
  surface color modes with invisible wide polyline for click targeting
- Click-to-split: click on route polyline inserts waypoint at nearest point,
  mapped to correct segment via boundary indices
- MidpointHandles: draggable CircleMarkers at route segment midpoints for
  reshaping, hidden below zoom 12, opaque on hover
- Color mode toggle (select) synced via Yjs routeData
- i18n keys for color mode labels (en + de)
- Unit tests for segment boundary tracking (13 tests)
- E2E tests for enriched route response and color mode toggle

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/i18n/src/locales/de.ts

@@ -54,6 +54,13 @@ export default {
     notes: {
       placeholder: "Notizen für diese Sitzung hinzufügen...",
     },
+    colorMode: {
+      label: "Routenfarbe",
+      plain: "Standard",
+      elevation: "Höhe",
+      surface: "Untergrund",
+      surfaceUnavailable: "Untergrunddaten für dieses Profil nicht verfügbar",
+    },
     rateLimitExceeded: "Zu viele Anfragen. Bitte versuche es später erneut.",
     elevation: {
       gain: "Höhenmeter aufwärts",

packages/i18n/src/locales/en.ts

@@ -54,6 +54,13 @@ export default {
     notes: {
       placeholder: "Add notes for this session...",
     },
+    colorMode: {
+      label: "Route Color",
+      plain: "Plain",
+      elevation: "Elevation",
+      surface: "Surface",
+      surfaceUnavailable: "Surface data not available for this profile",
+    },
     rateLimitExceeded: "Too many requests. Please try again later.",
     elevation: {
       gain: "Elevation Gain",