Fix _h_ema NameError; add status + article-draft notes

- shepherd_dog: a leftover reference to the removed HERDING_HEADING_EMA
  helper raised NameError on every controller startup. Drop it.
- docs/status.md: expand the n=5 mecanum failure-mode discussion with
  the four phantom-suppression attempts that didn't pan out, and the
  honest workaround (Webots reports n=10 only, n=5 covered by gym
  results).
- docs/article_draft.md: project-report outline with section structure,
  results tables, and the mecanum sim-to-real narrative for the
  formal writeup.

controllers/shepherd_dog/shepherd_dog.py

@@ -667,8 +667,7 @@ while robot.step(timestep) != -1:
                   f"tracks_cand={tracker.n_candidate()} "
                   f"tracks_penned={tracker.n_penned()} "
                   f"detections={len(detections)} "
-                  f"h={math.degrees(dog_heading):+.1f}°"
-                  + (f"→{math.degrees(dog_heading):+.1f}°" if _h_ema > 0 else ""))
+                  f"h={math.degrees(dog_heading):+.1f}°")
         if DRIVE_MODE == "mecanum":
             print(f"{common} action=({vx:+.2f}, {vy:+.2f}, {omega:+.2f})")
         else: