🐛 fix(calendar): use runtime config for cross-app service URLs

Calendar app was using $env/dynamic/public for TODO and Contacts API
URLs, which doesn't work in SPA mode. Updated to use runtime config:

- Add TODO_API_URL and CONTACTS_API_URL to runtime config
- Update docker-entrypoint.sh to include new env vars
- Refactor todos.ts and birthdays.ts to use lazy-loaded clients
- Refactor user-settings.svelte.ts with lazy store initialization
- Add env vars to docker-compose.staging.yml

This fixes staging deployment where cross-app integrations were
calling localhost instead of staging URLs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.staging.yml

@@ -319,6 +319,8 @@ services:
       # These vars are used by docker-entrypoint.sh to generate /config.json
       BACKEND_URL: https://calendar-api.staging.manacore.ai
       AUTH_URL: https://auth.staging.manacore.ai
+      TODO_API_URL: https://todo-api.staging.manacore.ai
+      CONTACTS_API_URL: https://contacts-api.staging.manacore.ai
     ports:
       - "5186:5186"
     healthcheck: