profile-weekly-distance: make the chart legible (axis, grid, tracks, hover)

Addresses feedback that a lone bar conveyed nothing. Rewrite WeeklyDistanceChart
as a proper SVG chart:
- y-scale topped at the busiest week with 0 / half / peak gridlines + km labels;
- faint per-week track columns so the 12-week axis is always visible (empty
  weeks read as gaps, not nothing — no more floating bar);
- oldest→newest date bounds on the x-axis;
- a hover readout naming the week + its distance ("Week of {{date}} · X km").

i18n adds profileStats.weekOf. Component test updated for the SVG structure
(bar per non-zero week, peak-topped scale, hover readout). typecheck + lint +
unit (journal 322) green; verified in the browser.

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

packages/i18n/src/locales/de.ts

@@ -416,6 +416,7 @@ export default {
       time: "Zeit",
       last4Weeks: "{{count}} in den letzten 4 Wochen",
       weeklyDistance: "Wochendistanz (letzte 12 Wochen)",
+      weekOf: "Woche vom {{date}}",
     },
     settings: {
       title: "Einstellungen",

packages/i18n/src/locales/en.ts

@@ -416,6 +416,7 @@ export default {
       time: "Time",
       last4Weeks: "{{count}} in the last 4 weeks",
       weeklyDistance: "Weekly distance (last 12 weeks)",
+      weekOf: "Week of {{date}}",
     },
     settings: {
       title: "Settings",