feat(ui): swap the in-turn loader for a brain-wave sweep left of the send button

Phase 117 (owner request, live-mockup-confirmed): the phase-109 3-dot
cue becomes a compact ECG trace (49px, P/QRS/T) with a brand sweep
traveling the path (bwdraw, 42/140 dash segment, 0.9s loop), the
loader repositioned left of the button so its appearance never shifts
it. setUiState stays the sole owner of the loader's hidden attribute;
the reduced-motion variant stills the sweep. Unit + lifecycle-E2E pins
updated for the new contract.

tests/e2e/test_turn_progress_loader.py

@@ -54,8 +54,9 @@ context, ``_reset_db`` reseeds the KB deterministically):
   ``SEND_STATUS`` idle shape (empty — not stuck on a mid-turn label);
   then, in a context with ``reducedMotion: "reduce"`` (the Playwright
   context option), a second turn shows the loader STILL visible
-  mid-turn — the reduced-motion variant stills the dots (computed
-  ``animation-name: none``), it does not HIDE the cue: visibility is
+  mid-turn — the reduced-motion variant stills the sweep (the phase-
+  117 brain wave: computed ``animation-name: none`` on the ``.bw-pulse``
+  path), it does not HIDE the cue: visibility is
   owned by the JS ``hidden`` attribute in ``setUiState`` (D16), not by
   CSS.
 """
@@ -281,13 +282,20 @@ def test_loader_a11y_and_reduced_motion(
     status = page.locator("#send-status")
     expect(status).to_have_attribute("aria-live", "polite")
     expect(status).to_have_text("")
-    # Control (default-motion context): the loader's dots run the
-    # typing animation — the reduced-motion check below stills it.
+    # Control (default-motion context): the CONTAINER carries no
+    # animation — the SWEEP path runs the phase-117 bwdraw travel —
+    # the reduced-motion check below stills it.
     assert (
         page.evaluate(
             "getComputedStyle(document.querySelector('#turn-loader')).animationName"
         )
-        == "typing"
+        == "none"
+    )
+    assert (
+        page.evaluate(
+            "getComputedStyle(document.querySelector('#turn-loader .bw-pulse')).animationName"
+        )
+        == "bwdraw"
     )
 
     # Reduced motion: a FRESH context with ``reducedMotion: "reduce"``
@@ -308,12 +316,13 @@ def test_loader_a11y_and_reduced_motion(
         # loader is still the visible cue ...
         expect(rm_page.locator(".tool-call")).to_be_visible(timeout=30_000)
         expect(rm_page.locator("#turn-loader")).to_be_visible()
-        # ... and the reduced-motion CSS variant IS applied: static
-        # dots, no pulse (the animation is gone from the computed
-        # style — the element itself is unchanged).
+        # ... and the reduced-motion CSS variant IS applied: the full
+        # trace shows static, no travel (the animation is gone from
+        # the sweep path's computed style — the loader itself is
+        # unchanged).
         assert (
             rm_page.evaluate(
-                "getComputedStyle(document.querySelector('#turn-loader')).animationName"
+                "getComputedStyle(document.querySelector('#turn-loader .bw-pulse')).animationName"
             )
             == "none"
         )