refactor: simplify expand chat input to 2-state with optimized button layout

- Remove 3-state logic (normal/50%/80%) - now only normal/expanded
- Remove double-click detection and tooltips for simplicity
- Remove platform-specific behavior (same UX for Electron and web)
- Optimize button layout: reduce from 36px to 28px to fit 3 buttons
- Position expand button above history buttons in vertical stack
- Keep 15-line expanded height (360px, capped to available space)

Per upstream dev feedback to keep it simple with one approach

packages/ui/src/styles/messaging/prompt-input.css

@@ -37,18 +37,18 @@
   height: 100%;
 }
 
- .prompt-input {
-   @apply w-full pl-3 pr-10 pt-2.5 border text-sm resize-none outline-none transition-colors;
-   font-family: inherit;
-   background-color: var(--surface-base);
-   color: inherit;
-   border-color: var(--border-base);
-   line-height: var(--line-height-normal);
-   border-radius: 0;
-   padding-bottom: 0;
-   height: 100%;
-   min-height: 100%;
- }
+.prompt-input {
+  @apply w-full pl-3 pr-10 pt-2.5 border text-sm resize-none outline-none transition-colors;
+  font-family: inherit;
+  background-color: var(--surface-base);
+  color: inherit;
+  border-color: var(--border-base);
+  line-height: var(--line-height-normal);
+  border-radius: 0;
+  padding-bottom: 0;
+  height: 100%;
+  min-height: 100%;
+}
 
 
 .prompt-input-overlay {
@@ -70,110 +70,47 @@
   color: var(--text-primary);
 }
 
-.prompt-history-top,
-.prompt-history-bottom {
+/* Navigation buttons container (expand, prev, next) */
+.prompt-nav-buttons {
   position: absolute;
-  right: 0.35rem;
+  top: 0.25rem;
+  right: 0.25rem;
+  bottom: 0.25rem;
   display: flex;
-  align-items: center;
-  justify-content: center;
+  flex-direction: column;
+  justify-content: flex-start;
+  gap: 0.125rem;
   z-index: 2;
 }
 
-.prompt-history-top {
-  top: 0.3rem;
-}
-
-.prompt-history-bottom {
-  bottom: 0.6rem;
-}
-
+.prompt-expand-button,
 .prompt-history-button {
-  @apply w-9 h-9 flex items-center justify-center rounded-md;
+  @apply w-7 h-7 flex items-center justify-center rounded-md;
   color: var(--text-muted);
   background-color: rgba(15, 23, 42, 0.04);
   transition: background-color 0.15s ease, color 0.15s ease;
   padding: 0;
+  flex-shrink: 0;
 }
 
+.prompt-expand-button:hover:not(:disabled),
 .prompt-history-button:hover:not(:disabled) {
   background-color: var(--surface-secondary);
   color: var(--text-primary);
 }
 
-.prompt-history-button:disabled {
-  opacity: 0.4;
-  cursor: not-allowed;
-}
-
-.prompt-expand-top {
-  position: absolute;
-  top: 0.3rem;
-  right: 3.5rem;
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  z-index: 2;
-}
-
-.prompt-expand-button {
-  @apply w-9 h-9 flex items-center justify-center rounded-md;
-  color: var(--text-muted);
-  background-color: rgba(15, 23, 42, 0.04);
-  transition: background-color 0.15s ease, color 0.15s ease;
-  padding: 0;
-  position: relative;
-}
-
-.prompt-expand-button:hover:not(:disabled) {
-  background-color: var(--surface-secondary);
-  color: var(--text-primary);
-}
-
 .prompt-expand-button:active:not(:disabled) {
   background-color: var(--accent-primary);
   color: var(--text-inverted);
   transform: scale(0.95);
 }
 
-.prompt-expand-button:disabled {
+.prompt-expand-button:disabled,
+.prompt-history-button:disabled {
   opacity: 0.4;
   cursor: not-allowed;
 }
 
-.prompt-expand-button::after {
-  content: attr(data-tooltip);
-  position: absolute;
-  top: calc(100% + 8px);
-  right: 0;
-  background: linear-gradient(135deg, rgba(30, 41, 59, 0.95) 0%, rgba(15, 23, 42, 0.98) 100%);
-  color: var(--text-primary);
-  padding: 0.5rem 0.75rem;
-  border-radius: 6px;
-  font-size: 0.75rem;
-  line-height: 1.4;
-  white-space: nowrap;
-  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.25), 0 0 0 1px rgba(255, 255, 255, 0.1);
-  border: 1px solid var(--border-base);
-  pointer-events: none;
-  opacity: 0;
-  transform: translateY(-4px);
-  transition: opacity 0.2s ease, transform 0.2s ease;
-  z-index: 1000;
-  backdrop-filter: blur(8px);
-}
-
-/* Only show tooltip on hover for Electron (desktop-mode) */
-.prompt-expand-button.desktop-mode:hover::after {
-  opacity: 1;
-  transform: translateY(0);
-}
-
-/* Web/Mobile: No tooltip (data-tooltip will be undefined anyway) */
-.prompt-expand-button.web-mode::after {
-  display: none;
-}
-
 .prompt-overlay-text {
   display: inline-flex;
   align-items: center;
@@ -369,4 +306,4 @@
     gap: 0;
     padding: 0;
   }
-}
+}