Replace North American ringback/busy tones with French standard
(440 Hz single tone with 1.5s/3.5s and 0.5s/0.5s cadences).
Fix a crash in on_playing_done where the error/cancel path freed
the MediaPlaybackData via g_autoptr without clearing the owning
pointer (data_calling/data_busy), leaving a dangling pointer that
would segfault on the next stop call.
Most desktop Linux sound themes lack telephony events like
phone-outgoing-calling and phone-outgoing-busy, causing gsound
playback to fail silently. Bundle OGG Vorbis fallback files and
pass GSOUND_ATTR_MEDIA_FILENAME alongside GSOUND_ATTR_EVENT_ID
so libcanberra falls back to the bundled audio when the theme
event is not found.