agent ui: input lives in terminal section, banner shimmer on activity

agent page restructure:
- send form moves into the terminal panel as a prompt-style row beneath
  the live tail (status line stays above so it still reads as a header).
- live panel + prompt share a single bordered 'terminal-wrap' box.
- harness-alive / login-state status lines drop their decorative ascii
  bookends; just a leading dot/glyph remains.
- banner gradient is now a real css gradient with a shimmer animation
  toggled by an .active class. turn_start adds it, turn_end removes it.
  dashboard side mirrors this: each broker sse event nudges a 4s
  shimmer window.
- dashboard container rows drop their static ▓█▓▒░ / ▒░▒░░ glyph
  prefixes; the role chips already disambiguate m1nd vs ag3nt.
- empty-state placeholders drop the ▓ bookends.

terminal pre-fill: hive-ag3nt::events::Bus grows a 500-event ring
buffer; new GET /events/history endpoint returns it. The agent JS
fetches history before opening the SSE stream so opening the page mid-
turn shows the last N events instead of a blank panel. The replay
walks turn_start/turn_end pairs to seed the banner-active state
correctly if a turn was still open.

hive-c0re/assets/dashboard.css

@@ -24,12 +24,29 @@ body {
   line-height: 1.6;
 }
 .banner {
-  color: var(--purple);
   text-align: center;
   margin: 0 0 1em 0;
   font-size: 0.95em;
-  text-shadow: 0 0 6px rgba(203, 166, 247, 0.55), 0 0 14px rgba(203, 166, 247, 0.25);
   overflow-x: auto;
+  background: linear-gradient(
+    90deg,
+    var(--purple-dim) 0%,
+    var(--purple) 50%,
+    var(--purple-dim) 100%
+  );
+  background-size: 200% 100%;
+  background-position: 50% 0;
+  -webkit-background-clip: text;
+  background-clip: text;
+  color: transparent;
+  filter: drop-shadow(0 0 6px rgba(203, 166, 247, 0.45));
+}
+.banner.active {
+  animation: banner-shimmer 1.8s linear infinite;
+}
+@keyframes banner-shimmer {
+  from { background-position: 200% 0; }
+  to   { background-position: -100% 0; }
 }
 h1, h2 {
   color: var(--purple);