fix(ui): stabilize workplace chat scrolling

opc/plugins/office_ui/frontend_src/chat/chat.css

@@ -794,6 +794,16 @@
 /* ══════════════════════════════════════════════════════════════════════════
    Message List
    ══════════════════════════════════════════════════════════════════════════ */
+.msg-list-shell {
+  flex: 1;
+  min-height: 0;
+  min-width: 0;
+  position: relative;
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+}
+
 .msg-list {
   flex: 1;
   min-height: 0;
@@ -803,16 +813,82 @@
   scrollbar-gutter: stable;
   scrollbar-color: var(--border) transparent;
   overscroll-behavior-y: contain;
-  overflow-anchor: none;
   position: relative;
 }
 
+.msg-list:focus {
+  outline: none;
+}
+
+.msg-list-following {
+  overflow-anchor: none;
+}
+
+.msg-list-browsing {
+  overflow-anchor: auto;
+}
+
+.msg-list-content {
+  width: 100%;
+  min-height: 100%;
+}
+
+.msg-timeline-row {
+  overflow-anchor: auto;
+}
+
+.msg-list-following .msg-timeline-row {
+  overflow-anchor: none;
+}
+
 .msg-end-anchor {
   height: 1px;
   flex-shrink: 0;
   overflow-anchor: none;
 }
 
+.msg-list-floating-actions {
+  position: absolute;
+  left: 50%;
+  bottom: 12px;
+  z-index: 8;
+  transform: translateX(-50%);
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  max-width: calc(100% - 24px);
+  pointer-events: none;
+}
+
+.msg-list-float-btn {
+  pointer-events: auto;
+  min-width: 0;
+  max-width: min(320px, 70vw);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  border: 1px solid color-mix(in srgb, var(--border) 72%, var(--accent) 28%);
+  border-radius: 999px;
+  padding: 7px 12px;
+  background: color-mix(in srgb, var(--bg-elevated) 92%, var(--accent) 8%);
+  color: var(--text);
+  box-shadow: 0 6px 22px rgba(0, 0, 0, 0.28);
+  font: inherit;
+  font-size: 11px;
+  font-weight: 600;
+  cursor: pointer;
+}
+
+.msg-list-float-btn:hover {
+  border-color: var(--accent);
+  background: color-mix(in srgb, var(--bg-elevated) 84%, var(--accent) 16%);
+}
+
+.msg-list-pending-btn {
+  border-color: color-mix(in srgb, var(--yellow) 55%, var(--border));
+  color: var(--yellow);
+}
+
 .msg-history-hint {
   display: flex;
   align-items: center;
@@ -849,33 +925,6 @@
   color: var(--text-secondary);
 }
 
-.msg-pending-section {
-  margin-top: 10px;
-  padding: 12px 16px 0;
-  border-top: 1px solid var(--border);
-  background: linear-gradient(180deg, transparent 0%, var(--bg-elevated) 28px);
-}
-
-.msg-pending-header {
-  font-size: 10px;
-  font-weight: 700;
-  color: var(--text-secondary);
-  text-transform: uppercase;
-  letter-spacing: 0.08em;
-  margin: 0 8px 10px;
-}
-
-.msg-pending-stack {
-  display: flex;
-  flex-direction: column;
-  gap: 10px;
-  padding-bottom: 8px;
-}
-
-.msg-row-pending {
-  animation: msg-enter 200ms ease-out;
-}
-
 /* ── Welcome ──────────────────────────────────────────────────────────── */
 .msg-welcome {
   display: flex;