MediaRecorder codec probe

Run this on the failing device (iOS Safari). For each H.264 profile string we checkisTypeSupported, record a 2-second clip, and inspect the bytes for theavc1 vshvc1 codec — catching Safari's "claims supported, emits HEVC anyway" trap.

Tip: copy the winning mime string from the green banner above and send it back — that becomes the one-line recorder fix.