UI: flip bubble hierarchy — responses elevated, prompts recessed

Design direction: "Illuminated Transcript" — the AI response is the
primary artifact; user prompts are subordinate margin notes.

ChatMessage.vue:
- User bubble: ghosted background (rgba 3-4% opacity), muted text,
  thin near-invisible border. De-emphasized, recessed.
- Assistant bubble: left indigo accent border (2px), elevated shadow
  via --color-bubble-asst-shadow. Commands attention.
- Assistant role label: indigo (var(--color-primary)); user label muted.
- Removed old white-override content rules (no longer on dark bg).
- Thinking block: full border → left-only indigo accent bar (35% opacity),
  removed inner top border.

ChatView.vue:
- Streaming bubble: same left accent + shadow as assistant bubbles.
- Streaming role label: indigo to match ChatMessage.
- Thinking block in streaming: same treatment as ChatMessage.

theme.css:
- Added --color-bubble-user-bg/border/text for light + dark.
- Added --color-bubble-asst-shadow for light + dark.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/assets/theme.css

@@ -38,6 +38,10 @@
   --color-input-bar-text: #1a1a1a;
   --color-input-bar-placeholder: rgba(0, 0, 0, 0.4);
   --color-overlay: rgba(0, 0, 0, 0.45);
+  --color-bubble-user-bg: rgba(0, 0, 0, 0.04);
+  --color-bubble-user-border: rgba(0, 0, 0, 0.08);
+  --color-bubble-user-text: #555566;
+  --color-bubble-asst-shadow: 0 2px 16px rgba(99, 102, 241, 0.10), 0 1px 4px rgba(0, 0, 0, 0.06);
   --radius-sm: 6px;
   --radius-md: 12px;
   --radius-lg: 18px;
@@ -85,6 +89,10 @@
   --color-input-bar-text: #e4e4f0;
   --color-input-bar-placeholder: rgba(228, 228, 240, 0.35);
   --color-overlay: rgba(0, 0, 0, 0.65);
+  --color-bubble-user-bg: rgba(255, 255, 255, 0.03);
+  --color-bubble-user-border: rgba(255, 255, 255, 0.07);
+  --color-bubble-user-text: #5a5a72;
+  --color-bubble-asst-shadow: 0 4px 28px rgba(99, 102, 241, 0.14), 0 2px 8px rgba(0, 0, 0, 0.4);
 }
 
 *,

frontend/src/components/ChatMessage.vue

@@ -121,13 +121,19 @@ const timingParts = computed((): string[] => {
   border-radius: 18px;
 }
 
+/* User prompts: recessed, muted — margin notes */
 .role-user .message-bubble {
-  background: linear-gradient(135deg, #6366f1, #4f46e5);
-  color: #fff;
+  background: var(--color-bubble-user-bg);
+  border: 1px solid var(--color-bubble-user-border);
+  color: var(--color-bubble-user-text);
   border-bottom-right-radius: 4px;
 }
+
+/* Assistant responses: elevated, lit — the primary text */
 .role-assistant .message-bubble {
   background: var(--color-bg-card);
+  border-left: 2px solid var(--color-primary);
+  box-shadow: var(--color-bubble-asst-shadow);
   border-bottom-left-radius: 4px;
 }
 
@@ -144,16 +150,17 @@ const timingParts = computed((): string[] => {
   letter-spacing: 0.03em;
 }
 .role-user .role-label {
-  color: rgba(255, 255, 255, 0.7);
+  color: var(--color-text-muted);
+  opacity: 0.6;
 }
 .role-assistant .role-label {
-  color: var(--color-text-muted);
+  color: var(--color-primary);
 }
 
 .thinking-block {
   margin-bottom: 0.5rem;
-  border: 1px solid var(--color-border);
-  border-radius: var(--radius-sm);
+  border-left: 2px solid rgba(129, 140, 248, 0.35);
+  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
   overflow: hidden;
 }
 .thinking-summary {
@@ -191,7 +198,6 @@ details[open] .thinking-summary::before {
   max-height: 300px;
   overflow-y: auto;
   background: var(--color-bg-secondary);
-  border-top: 1px solid var(--color-border);
 }
 .message-content {
   font-size: 0.95rem;
@@ -202,22 +208,6 @@ details[open] .thinking-summary::before {
   margin-bottom: 0;
 }
 
-/* User bubble content overrides for readability on primary bg */
-.role-user .message-content :deep(a) {
-  color: rgba(255, 255, 255, 0.9);
-  text-decoration: underline;
-}
-.role-user .message-content :deep(code) {
-  background: rgba(255, 255, 255, 0.15);
-  color: #fff;
-}
-.role-user .message-content :deep(pre) {
-  background: rgba(0, 0, 0, 0.2);
-}
-.role-user .message-content :deep(blockquote) {
-  border-left-color: rgba(255, 255, 255, 0.4);
-  color: rgba(255, 255, 255, 0.85);
-}
 
 .message-actions {
   display: flex;

frontend/src/views/ChatView.vue

@@ -1222,6 +1222,8 @@ onUnmounted(() => {
   border-radius: 18px;
   border-bottom-left-radius: 4px;
   background: var(--color-bg-card);
+  border-left: 2px solid var(--color-primary);
+  box-shadow: var(--color-bubble-asst-shadow);
 }
 .streaming-bubble .message-header {
   display: flex;
@@ -1231,7 +1233,7 @@ onUnmounted(() => {
 .streaming-bubble .role-label {
   font-size: 0.75rem;
   font-weight: 600;
-  color: var(--color-text-muted);
+  color: var(--color-primary);
   text-transform: uppercase;
   letter-spacing: 0.03em;
 }
@@ -1258,8 +1260,8 @@ onUnmounted(() => {
 }
 .thinking-block {
   margin-bottom: 0.5rem;
-  border: 1px solid var(--color-border);
-  border-radius: var(--radius-sm);
+  border-left: 2px solid rgba(129, 140, 248, 0.35);
+  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
   overflow: hidden;
 }
 .thinking-summary {
@@ -1297,7 +1299,6 @@ details[open] .thinking-summary::before {
   max-height: 300px;
   overflow-y: auto;
   background: var(--color-bg-secondary);
-  border-top: 1px solid var(--color-border);
 }
 .streaming-status-dot {
   display: inline-block;