feat: add EU region support to companion apps

[PeerRich]

Summary

Enables cal.eu alongside cal.com across the companion mobile app and browser extension. Users pick a data region on the login screen; from that point onward the app uses region-scoped OAuth, API, and deep-link hosts.

Mobile app

• New apps/mobile/utils/region.ts — persists us/eu in generalStorage, exposes synchronous getRegion(), async setRegion()/preloadRegion(), a subscribeRegion() listener, and helpers getCalAppUrl() / getCalApiUrl() / getCalWebUrl() plus a CAL_APP_HOSTNAMES set for host checks.
• LoginScreen.tsx — adds a "Data region" dropdown (United States / European Union), preloads the region on mount, subscribes to changes, and makes the "Sign up" link region-aware.
• AuthContext.tsx — preloads the region on app startup and recreates the OAuth service whenever the region changes so subsequent authorization flows target the correct cal.{com|eu}.
• oauthService.ts — calcomBaseUrl now comes from getCalAppUrl(region). Each browser's OAuth config (iOS WebAuth, Firefox, Safari, Edge) reads region-scoped env vars (..._EU variants) with fallback to the US values.
• services/calcom/request.ts — replaces the hardcoded API_BASE_URL with getApiBaseUrl() so every authenticated API call routes to api.cal.com or api.cal.eu.
• Deep links, in-app browser, WebAuth callbacks, profile sheet, and the More tab — now recognize both app.cal.com and app.cal.eu hosts and build URLs from getCalAppUrl().

Extension

• wxt.config.ts — adds https://app.cal.eu/* and https://api.cal.eu/* to host_permissions and plumbs EU OAuth env vars (base + Firefox/Safari/Edge variants) into the Vite define so the mobile code running in the iframe can read them.
• entrypoints/content.ts + entrypoints/background/index.ts — the iframe forwards the selected region alongside OAuth tokens on sync; the background persists it in extension storage and derives its API_BASE_URL per-request so validateTokens, fetchEventTypes, getBookingStatus, and markAttendeeNoShow all hit the correct regional API. Clearing tokens also clears the stored region.

New env vars (unset = fall back to the US values):

• EXPO_PUBLIC_CALCOM_OAUTH_CLIENT_ID_EU
• EXPO_PUBLIC_CALCOM_OAUTH_REDIRECT_URI_EU
• ..._FIREFOX_EU, ..._SAFARI_EU, ..._EDGE_EU variants

Review & Testing Checklist for Human

• Provision the EXPO_PUBLIC_CALCOM_OAUTH_*_EU env vars in the deployment / extension build pipeline before shipping; without them EU users silently fall back to the US client IDs and the redirect to app.cal.eu will fail.
• End-to-end login as a US user: verify OAuth still redirects through app.cal.com, tokens are minted against api.cal.com, and post-login API calls go to api.cal.com.
• End-to-end login as an EU user: pick "European Union" on the login screen, verify OAuth redirects through app.cal.eu, tokens are minted against api.cal.eu, and post-login API calls go to api.cal.eu (check Network tab / extension service worker logs).
• Region switching: log out, switch region, log back in — confirm the OAuth service is recreated and the new region sticks across app restarts.
• Extension: with an EU session active, confirm validateTokens succeeds on app resume (would fail silently if it still hit api.cal.com) and that fetch-event-types / getBookingStatus return EU data.
• Extension "Delete Account" and other openInAppBrowser deep links point at the correct host for the selected region.

Notes

• cal.com/help/... and cal.com/roadmap marketing URLs are intentionally left on .com (not region-scoped content).
• Icon/image URLs served off app.cal.com in locationHelpers.ts, defaultLocations.ts, and getAppIconUrl.ts are also left alone — they're public static assets and not part of the auth/API surface. Happy to make them region-aware in a follow-up if the EU CDN serves the same paths.
• PR is slightly over the 10-file soft limit (18 files) because region plumbing is a cross-cutting change; splitting it would leave the app in half-migrated states. Most files are small host-substitution edits.

Link to Devin session: https://app.devin.ai/sessions/ed4320aeeb174166b9bd2c995f9ec364
Requested by: @PeerRich

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR that start with 'DevinAI' or '@devin'.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring