feat(planner): collapsible elevation chart with summary bar

Docked-but-collapsible placement (the chosen direction):

- A collapse toggle (chevron) in the chart header; state persists to
  localStorage.
- Collapsed = a thin summary bar: a mini sage sparkline + distance and
  ascent/descent + an expand toggle. Reclaims map space on demand.
- Summary figures come from the same authoritative routeStats the
  sidebar uses (distance, elevationGain, elevationLoss), so the numbers
  match the sidebar exactly — not recomputed from the raw elevation
  points (which over-counted ascent ~2x from noise).

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

packages/i18n/src/locales/de.ts

@@ -139,6 +139,8 @@ export default {
       bikeroute: "Radroutenprofil",
       low: "Tief",
       high: "Hoch",
+      collapse: "Höhenprofil einklappen",
+      expand: "Höhenprofil ausklappen",
     },
     landing: {
       startPlanning: "Planung starten",

packages/i18n/src/locales/en.ts

@@ -139,6 +139,8 @@ export default {
       bikeroute: "Bike Route Profile",
       low: "Low",
       high: "High",
+      collapse: "Collapse elevation profile",
+      expand: "Expand elevation profile",
     },
     landing: {
       startPlanning: "Start Planning",