fix(exports): keep callbacks that other resources pass through an export

[Github-Samuel]

Summary

A function handed to an export by another resource arrives as a function reference: a table with a __call metamethod, not a Lua function. #304 fixed this for Bluetooth devices. The same type(x) == 'function' check sat on every other export that takes a callback, so the callback was dropped for exactly the callers those exports exist for:

• uploadMedia returned false for any outside caller and never answered.
• showLockscreenWidget dropped onAction, so the owning resource never heard a tap.
• addCustomApp dropped onOpen / onUse / onClose / onDelete.
• The lb-phone SendMessage shim skipped its callback, and the qs registerCallInterceptor shim refused the registration.

Changes

• New shared/callable.lua with callable.is(value): a Lua function, or a table whose metatable has __call.
• Every export above now uses it. Bluetooth uses the same helper instead of its own copy from fix(bluetooth): keep onConnect/onDisconnect passed through the export #304.
• Internal registrars (util.onCleanup, target.onReady, job.onChange, media.registerFeature) only ever see real functions and are unchanged.
• Corrects the roadphone kill switch name in the loader comment (sd_phone_roadphonecompat), reported in NUI → server HTTP upload hangs ~60 s on FiveM for GTAV Enhanced before falling back #297.

Testing

Live on a QBox dev server, calling from a second resource:

• Confirmed the shape: a function crossing a resource boundary is type = table with __call.
• uploadMedia: before, returned false and the callback never ran. After, the callback receives Expected a base64 data: URL. A plain table is still refused.
• Bluetooth: onConnect and onDisconnect (reason kicked) both fire.
• Custom app: onOpen, onClose and onDelete fire on their lifecycle actions.
• Lock screen widget: onAction receives the action and its value.

Not exercised: the two compat shim callbacks.

Lua suite: 597 passed, with the same two suite errors as main (port_settings_test, port_photogram_test). The new callable cases fail when the helper is reverted to the function-only check.

Breaking Changes

None. Plain Lua functions pass as before; anything that is neither a function nor callable is still ignored.