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>

README.md

@@ -12,7 +12,8 @@ Job Tracker is a simple, self-hosted app for tracking job applications with a Re
 - History/event trail per application (created, status changes, follow-up set, delete/restore)
 - Export jobs to JSON/CSV + daily scheduled JSON export
 - Optional “job import” preview from supported job sites (plugins) + optional translation to English
-- Quick-capture bookmarklet (Settings): opens `/?add=<page url>` to pre-fill Add Job from any posting
+- Quick-capture bookmarklet (Settings) + installable PWA with a mobile share-target: both open `/?add=<page url>` to pre-fill Add Job from any posting
+  - Note: no offline service-worker cache is bundled by design (the app is deployed frequently; an aggressive cache would risk serving stale builds). The manifest provides installability and share-to-capture without it.
 - Optional local AI service for short/full descriptions
 - Optional Google sign-in (Google ID tokens) to protect the API