feat: installable PWA with mobile share-target capture

- Corrected manifest (Jobbjakt branding, matching green theme, maskable
  icons, description/categories/scope/id).
- share_target (GET) maps a shared url/link into the same /?add= capture
  flow the bookmarklet uses, so mobile 'Share -> Jobbjakt' pre-fills Add
  Job.
- resolveCaptureUrl helper (tested) extracts the link from add or from a
  link embedded in shared text; App uses it and strips the params.
- Deliberately no offline service worker: the app deploys frequently and
  an aggressive cache would risk stale builds (documented in README).
- 4 unit tests; build compiles.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

job-tracker-ui/src/captureUrl.test.ts

@@ -0,0 +1,22 @@
+import { resolveCaptureUrl } from './captureUrl';
+
+describe('resolveCaptureUrl', () => {
+  test('reads the bookmarklet add param', () => {
+    expect(resolveCaptureUrl('?add=https%3A%2F%2Fexample.com%2Fjob')).toBe('https://example.com/job');
+  });
+
+  test('extracts a url embedded in shared text', () => {
+    expect(resolveCaptureUrl('?addtext=' + encodeURIComponent('Cool role here https://example.com/job/42 apply now')))
+      .toBe('https://example.com/job/42');
+  });
+
+  test('prefers add over addtext', () => {
+    expect(resolveCaptureUrl('?add=https%3A%2F%2Fa.com&addtext=' + encodeURIComponent('https://b.com')))
+      .toBe('https://a.com');
+  });
+
+  test('returns null when there is no url', () => {
+    expect(resolveCaptureUrl('')).toBeNull();
+    expect(resolveCaptureUrl('?addtext=' + encodeURIComponent('just some text, no link'))).toBeNull();
+  });
+});