ADD - check GitHub releases on startup (#10)

Compare the fxmanifest version against the latest published sky_phone release tag and report update, current, ahead, and failure states without blocking resource startup.

Document the startup check and cover the HTTP and version comparison behavior with a focused Lua test.

sky_phone/fxmanifest.lua

@@ -55,6 +55,7 @@ server_scripts {
     'config/media.lua',
     'config/locales/en.lua',
     'config/locales/de.lua',
+    'source/server/update_check.lua',
     'source/bridge/server/database.lua',
     'source/bridge/server/migrations.lua',
     'source/bridge/server/callbacks.lua',