Add Journal day breakdown and elevation chart dividers

- routes.server.ts: Extract dayBreaks from parsed GPX waypoints on save
- routes.$id.tsx: Compute per-day stats in loader, render day breakdown
  section with distance/ascent/descent per day
- ElevationChart: Dashed vertical lines at day boundaries
- i18n: Add Journal day breakdown keys (en + de)

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

packages/i18n/src/locales/de.ts

@@ -135,6 +135,8 @@ export default {
       delete: "Route löschen",
       distance: "Strecke",
       elevationGain: "Höhenmeter",
+      dayBreakdown: "Tagesübersicht",
+      dayLabel: "Tag {{n}}",
       noRoutesYet: "Noch keine Routen. Erstelle deine erste Route!",
       noMapPreview: "Keine Kartenvorschau",
       saveChanges: "Änderungen speichern",

packages/i18n/src/locales/en.ts

@@ -135,6 +135,8 @@ export default {
       delete: "Delete Route",
       distance: "Distance",
       elevationGain: "Elevation Gain",
+      dayBreakdown: "Day Breakdown",
+      dayLabel: "Day {{n}}",
       noRoutesYet: "No routes yet. Create your first route!",
       noMapPreview: "No map preview",
       saveChanges: "Save Changes",