refactor: replace rotation vector with body up vector for tilt input

- Replace body_attitude() with body_up_vector(): rotate world-up [0,0,1]
  by corrected world→body quaternion to get body up vector (pitch/roll only,
  no yaw). Matches DiffPhysDrone's env.R[:, 2] approach.
- Update ComputeTilt transform to use body_up_vector_np
- Update visualize_dataset.py to display Euler angles and body up vector
- Update model.py comments and disable CNN (zero output)
- Sync AGENTS.md with new architecture description

Generated by Mistral Vibe (ds-v4-flash).
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

visualize/visualize_dataset.py

@@ -24,7 +24,7 @@ import torch
 
 # Reuse the same coordinate transforms as the training pipeline
 from src.velocity_prediction.utils import (
-    body_attitude_np,
+    body_up_vector_np,
     quat_to_euler_np,
     world_vel_to_body_np,
     quat_normalize,
@@ -199,11 +199,11 @@ def draw_pose_overlay(
     ]
     put_text(euler_lines, origin=(10, 62), color=(0, 200, 255))
 
-    # ── Body attitude (rotation vector) ──
-    tilt_lines = [
-        f"Att:   rx={tilt[0]:+.3f}  ry={tilt[1]:+.3f}  rz={tilt[2]:+.3f}",
+    # ── Body up vector (pitch & roll only) ──
+    up_lines = [
+        f"Body up: ({tilt[0]:+.3f}, {tilt[1]:+.3f}, {tilt[2]:+.3f})",
     ]
-    put_text(tilt_lines, origin=(10, 104), color=(0, 200, 255))
+    put_text(up_lines, origin=(10, 104), color=(0, 200, 255))
 
     # ── Body-frame velocity ──
     v_right, v_forward = v_body  # [v_right, v_forward]
@@ -334,8 +334,8 @@ def create_video(
     for i, frame_data in enumerate(frames):
         q_raw = frame_data["pose"][3:7]  # [qx, qy, qz, qw]  world→odom
 
-        # True body attitude rotation vector (preserves yaw)
-        tilt = body_attitude_np(q_raw)  # (3,)
+        # Body up vector (pitch & roll only, no yaw) — matches DiffPhysDrone
+        body_up = body_up_vector_np(q_raw)  # (3,)  unit vector
 
         # Euler angles from body quaternion for display
         q_body = correct_attitude(q_raw)
@@ -349,7 +349,7 @@ def create_video(
             canvas=frame_data["img"],
             pose=frame_data["pose"],
             vel=frame_data["vel"],
-            tilt=tilt,
+            tilt=body_up,
             v_body=v_body,
             euler=euler_deg,
             frame_idx=i,