normalize media pipeline at client boundary

- AudioParams.framing field: client declares "raw" or "adts"
- Client strips ADTS from audio before sending (strip_adts)
- Client does H.264 NAL inspection for keyframe detection (h264_is_keyframe)
- Server uses declared sample_rate/channels for ADTS synthesis instead of hardcoded 48kHz/stereo
- Server gates ADTS wrapping on framing field instead of per-packet sniffing

New backends only need to pipe output to demux_and_send() — server and Python unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

media/common/src/protocol.rs

@@ -166,6 +166,14 @@ pub struct AudioParams {
     pub sample_rate: u32,
     pub channels: u16,
     pub codec: String,
+    /// Audio framing on the wire: "raw" (no container headers) or "adts".
+    /// Default "raw" — client strips ADTS before sending.
+    #[serde(default = "default_framing")]
+    pub framing: String,
+}
+
+fn default_framing() -> String {
+    "raw".into()
 }
 
 impl ControlMessage {
@@ -231,6 +239,7 @@ mod tests {
                 sample_rate: 48000,
                 channels: 2,
                 codec: "aac".into(),
+                framing: "raw".into(),
             },
         };
         let wire = msg.to_wire_packet().unwrap();