Deepen three architectural seams: FIT consolidation, host election extraction, injectable db

- Extract shared fitToGpx into connected-services/fit.ts (FIT is a Garmin
  open standard used by Wahoo, Coros, Garmin — not provider-specific)
- Add importActivity() to sync/imports.server.ts so providers call one
  function instead of createActivity + recordImport separately; eliminates
  direct dependency on activities.server.ts from provider adapters
- Update wahoo importer + webhook to use both shared helpers
- Extract useHostElection(yjs) hook from useRouting so host election is
  independently testable without mounting the full routing stack
- Add setDb() to journal db.ts for module-level injection in unit tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/journal/app/lib/connected-services/fit.ts

@@ -0,0 +1,38 @@
+// Shared FIT file → GPX converter for provider importers.
+//
+// FIT is an open standard (Garmin/ANT+) used by Wahoo, Garmin, Coros, and
+// others. This module is shared across all providers that produce FIT files
+// so the conversion logic lives in one place.
+
+import FitParser from "fit-file-parser";
+import { generateGpx } from "@trails-cool/gpx";
+
+export async function fitToGpx(buffer: Buffer, name: string): Promise<string | null> {
+  const parsed = await new Promise<Record<string, unknown>>((resolve, reject) => {
+    const parser = new FitParser({ force: true });
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    parser.parse(buffer as any, (error: unknown, data: any) => {
+      if (error) reject(error);
+      else resolve(data ?? {});
+    });
+  });
+
+  const records = (parsed.records ?? []) as Array<{
+    position_lat?: number;
+    position_long?: number;
+    altitude?: number;
+    timestamp?: string | Date;
+  }>;
+
+  const trackPoints = records
+    .filter((r) => r.position_lat != null && r.position_long != null)
+    .map((r) => ({
+      lat: r.position_lat!,
+      lon: r.position_long!,
+      ele: r.altitude,
+      time: r.timestamp instanceof Date ? r.timestamp.toISOString() : r.timestamp,
+    }));
+
+  if (trackPoints.length < 2) return null;
+  return generateGpx({ name, tracks: [trackPoints] });
+}