feat(data-only): ingest /pose/hands into handFeat

Add OSCdef(\poseHands) to data_feeds.scd storing lx/ly/lopen/lspeed,
rx/ry/ropen/rspeed/dist into ~handFeat Dictionary (9 floats, pid=0).
Initialize ~handFeat alongside existing ~poseState/~poseKin.

Load scene_pose_action.scd in boot.scd after scenes.scd so ~mapPoseToFx
is defined at runtime (was silently dead before).

Document /pose/hands contract in data_only_viz/README.md.

data_only_viz/README.md

@@ -0,0 +1,13 @@
+# data_only_viz
+
+Python + Metal visualiser for the AV-Live data-only patch.
+
+## Hand features OSC
+
+`/pose/hands [pid=0, lx, ly, lopen, lspeed, rx, ry, ropen, rspeed, dist]`
+
+- Emitted once per pipeline tick by `pose_bridge.send_hands` to sclang `:57121`.
+- L = leftmost hand on screen, R = rightmost; absent hand -> its 4 floats are 0.
+- Ranges: positions/openness/dist in [0,1]; speed >= 0 (normalized units/frame).
+- Consumed by SuperCollider `~handFeat` (data_only) and the Metal renderer uniforms.
+- Multi-person is not yet carried (pid is always 0).

sound_algo/control/data_feeds.scd

@@ -465,6 +465,7 @@
 // =====================================================================
 ~poseState = ~poseState ? Dictionary.new;
 ~poseKin   = ~poseKin   ? Dictionary.new;
+~handFeat  = ~handFeat  ? Dictionary.new;
 
 OSCdef(\poseAction, { |msg|
     var pid = msg[1];
@@ -495,6 +496,18 @@ OSCdef(\poseLeave, { |msg|
     ~poseKin.removeAt(pid);
 }, '/pose/leave');
 
+OSCdef(\poseHands, { |msg|
+    ~handFeat[\lx]     = msg[2];
+    ~handFeat[\ly]     = msg[3];
+    ~handFeat[\lopen]  = msg[4];
+    ~handFeat[\lspeed] = msg[5];
+    ~handFeat[\rx]     = msg[6];
+    ~handFeat[\ry]     = msg[7];
+    ~handFeat[\ropen]  = msg[8];
+    ~handFeat[\rspeed] = msg[9];
+    ~handFeat[\dist]   = msg[10];
+}, '/pose/hands');
+
 "[OK] action-head OSC handlers".postln;
 
 "[data_feeds] OSCdef installes (USGS, SWPC, NETZ, RTE, BLITZ, OPENSKY, BSKY, MEMPOOL, GCN).".postln;

sound_algo/data_only/boot.scd

@@ -133,6 +133,10 @@ Routine({
     (~base ++ "scenes.scd").load;
     0.5.wait;
 
+    // -- 6b. Pose/hand -> FX mapping -----
+    (~base ++ "scene_pose_action.scd").load;
+    0.5.wait;
+
     // -- 7) Demarre la scene par defaut -----
     if(~doScene.isNil) {
         "[data-only/boot] ERREUR : ~doScene non defini".warn;