Implement shared packages (tasks 2.1-2.6)

- @trails-cool/types: Route, Activity, Waypoint, RouteVersion, RouteMetadata
- @trails-cool/gpx: GPX parser (XML→waypoints/tracks/elevation) and generator
  with round-trip test, haversine distance, elevation gain/loss computation
- @trails-cool/map: MapView (Leaflet + OSM/OpenTopoMap/CyclOSM layer switcher),
  RouteLayer (GeoJSON polyline rendering)
- @trails-cool/ui: Button (primary/secondary/ghost), Input (with label/error),
  Card components with Tailwind styling
- @trails-cool/i18n: react-i18next config with English + German translations,
  browser language detection, fallback to English

All 13 unit tests pass. Both apps build successfully.

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

packages/gpx/src/parse.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect } from "vitest";
+import { parseGpx } from "./parse";
+
+const sampleGpx = `<?xml version="1.0" encoding="UTF-8"?>
+<gpx version="1.1" creator="test" xmlns="http://www.topografix.com/GPX/1/1">
+  <metadata><name>Test Route</name></metadata>
+  <wpt lat="52.52" lon="13.405"><name>Berlin</name></wpt>
+  <wpt lat="48.137" lon="11.576"><name>Munich</name></wpt>
+  <trk>
+    <trkseg>
+      <trkpt lat="52.52" lon="13.405"><ele>34</ele></trkpt>
+      <trkpt lat="51.05" lon="13.74"><ele>113</ele></trkpt>
+      <trkpt lat="48.137" lon="11.576"><ele>519</ele></trkpt>
+    </trkseg>
+  </trk>
+</gpx>`;
+
+describe("parseGpx", () => {
+  it("parses route name", () => {
+    const result = parseGpx(sampleGpx);
+    expect(result.name).toBe("Test Route");
+  });
+
+  it("parses waypoints with lat, lon, and name", () => {
+    const result = parseGpx(sampleGpx);
+    expect(result.waypoints).toHaveLength(2);
+    expect(result.waypoints[0]).toEqual({ lat: 52.52, lon: 13.405, name: "Berlin" });
+    expect(result.waypoints[1]).toEqual({ lat: 48.137, lon: 11.576, name: "Munich" });
+  });
+
+  it("parses track points with elevation", () => {
+    const result = parseGpx(sampleGpx);
+    expect(result.tracks).toHaveLength(1);
+    expect(result.tracks[0]).toHaveLength(3);
+    expect(result.tracks[0]![0]).toEqual({ lat: 52.52, lon: 13.405, ele: 34, time: undefined });
+  });
+
+  it("computes elevation gain and loss", () => {
+    const result = parseGpx(sampleGpx);
+    expect(result.elevation.gain).toBeGreaterThan(0);
+    expect(result.elevation.loss).toBe(0); // monotonically increasing elevation
+    expect(result.elevation.gain).toBe(485); // 113-34 + 519-113
+  });
+
+  it("builds elevation profile", () => {
+    const result = parseGpx(sampleGpx);
+    expect(result.elevation.profile).toHaveLength(3);
+    expect(result.elevation.profile[0]!.distance).toBe(0);
+    expect(result.elevation.profile[0]!.elevation).toBe(34);
+    expect(result.elevation.profile[2]!.distance).toBeGreaterThan(0);
+  });
+
+  it("throws on invalid XML", () => {
+    expect(() => parseGpx("not xml at all <<<<")).toThrow("Invalid GPX XML");
+  });
+});