fix(walk): the cycle starts at maximum stride, so the capture shows one

The stride shot regressed twice for two different reasons, and only the second was
the clip. The walk cycle was authored on a sine, which is zero at both the start and
the middle of the cycle - exactly the two frames where the legs pass together - so a
deterministic capture at any phase near those frames read as a still. The probe
proved it: frames 0 and 15 carried identical hip rotations while 7 and 22 were the
stride.

The cycle now starts at maximum stride (cosine). Length, amplitudes, keys and loop
are unchanged; only the phase moved. demo-third-person-walk is back as shot 8 and
shows a genuine stride with the curled hands from 0.2.1.

8/8 shots verify.

Tools/visual_targets.json

@@ -84,6 +84,18 @@
         "Art/reference/hollywood/el-capitan-facade-day-wikimedia-2009-10-27.jpg"
       ],
       "expect": "Front view of the player body from the road: both arms hanging at the sides, hands down by the hips, face and chest visible, hero facade behind the camera"
+    },
+    {
+      "name": "demo-third-person-walk",
+      "shot": "Screenshots/demo/review-demo-third-person-walk.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/el-capitan-facade-day-wikimedia-2009-10-27.jpg"
+      ],
+      "expect": "The player body mid-stride in profile: legs apart, arms counter-swinging, walking along the sidewalk"
     }
   ]
 }