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>

src/pages/game/GameDialogs.jsx

@@ -6,6 +6,7 @@ import { RealIntroDialog } from './RealIntroDialog.jsx';
 import { InstallDialog } from './InstallDialog.jsx';
 import { UpdateNotice } from './UpdateNotice.jsx';
 import { EndDialog } from './EndDialog.jsx';
+import { GpsFallbackDialog } from './GpsFallbackDialog.jsx';
 /** Composes independently managed game dialogs. */
 export function GameDialogs(props) {
   return (
@@ -18,6 +19,7 @@ export function GameDialogs(props) {
       <InstallDialog {...props} />
       <UpdateNotice {...props} />
       <EndDialog {...props} />
+      <GpsFallbackDialog {...props} />
     </>
   );
 }