feat: add landing-style start screen with four start modes

Phase 3 of turning the game into the company landing page.

- Replace the Iran-map briefing with a brand start screen over the
  orbiting 3D factory: logo, tagline and four ways in.
- Real world: safety notice, then GPS; if location is denied or
  missing, a friendly dialog offers offline play instead.
- Offline: start at Park Mellat beside the family car with the route
  to the factory, where the first purchase mission is.
- About Us: start in the factory yard. Products: start at the machine
  samples with the showroom open.
- Contact, address with map links, FAQ, careers, gallery and social
  links open in a sheet (bottom sheet on phones) from company config.
- Restart replays the chosen mode. Layout scrolls on short screens and
  respects safe areas.
- Add tests for the start screen, map links and theme.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/content.test.js

@@ -69,6 +69,6 @@ test('Brand palette keeps readable contrast', () => {
 test('Strings that take values build complete sentences', () => {
   assert.equal(strings.prompts.getIn('بی‌ام‌و'), 'F · سوار بی‌ام‌و شو');
   assert.equal(strings.units.hetoman('۵۰۰'), '۵۰۰ هتومان');
-  assert.ok(strings.briefing.subtitle.includes(COMPANY.shortName));
+  assert.ok(strings.landing.logoAlt.includes(COMPANY.shortName));
   assert.equal(strings.ranks.length, 6);
 });