profile-stats: lifetime roll-up header on the profile

Implements the profile-stats change (specs/profile-stats):

- getActivityStats(ownerId, { publicOnly }) in activities.server.ts: one indexed
  aggregate over stored columns (count, sum distance/ascent/elapsed duration) +
  a rolling last-4-weeks count. No cache table, no schema change, no GPX parsing
  (design §D1).
- Profile loader computes it scoped to the viewer (public-only for visitors,
  full totals for the owner); ProfileStats header renders count · distance ·
  ascent · time + "N in the last 4 weeks" via the shared StatRow + stats.ts
  formatters; hidden when there are no visible activities.
- i18n journal.profileStats.* in en + de.

Tests: ProfileStats component (jsdom: totals, empty, last-4-weeks toggle);
e2e asserts the owner roll-up counts their activities. typecheck + lint + unit
(journal 318) green; verified in the browser.

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

playwright.config.ts

@@ -138,6 +138,14 @@ export default defineConfig({
         baseURL: "http://localhost:3000",
       },
     },
+    {
+      name: "profile-stats",
+      testMatch: "profile-stats.test.ts",
+      use: {
+        ...devices["Desktop Chrome"],
+        baseURL: "http://localhost:3000",
+      },
+    },
   ],
   webServer: process.env.CI
     ? [