feat(ui): terminal, charts and low-contrast text follow the selected theme

- The lane terminal (xterm) takes its palette from the selected DARK theme —
  it stays dark in light mode, as a terminal should — and repaints live when
  the theme changes (`client/src/lib/terminalTheme.ts`).
- Charts on the Dashboard and Workflows pages draw their grid, axes, labels
  and tooltips from theme tokens instead of hardcoded near-black/white, and
  the activity heatmap ramps from the page surface to the accent, so it reads
  on every theme instead of going near-black on light ones.
- Status/brand text that only worked on dark backgrounds
  (`text-*-300/400`) gets a darker light-mode shade (`text-*-700
  dark:text-*-300`) across sessions, conversations, workflows, config and
  settings. Categorical chart colours are kept.

client/src/components/conversation/MessageList.tsx

@@ -82,25 +82,25 @@ const SENDER_STYLES: Record<
     label: "User",
     icon: User,
     avatarRing:
-      "bg-gradient-to-br from-blue-600/30 to-cyan-500/20 text-blue-300 ring-1 ring-blue-500/30",
+      "bg-gradient-to-br from-blue-600/30 to-cyan-500/20 text-blue-700 dark:text-blue-300 ring-1 ring-blue-500/30",
     accentBar: "before:bg-blue-600/40",
-    headerText: "text-blue-300",
+    headerText: "text-blue-700 dark:text-blue-300",
   },
   assistant: {
     label: "Assistant",
     icon: Bot,
     avatarRing:
-      "bg-gradient-to-br from-violet-500/30 to-fuchsia-500/20 text-violet-200 ring-1 ring-violet-400/30",
+      "bg-gradient-to-br from-violet-500/30 to-fuchsia-500/20 text-violet-800 dark:text-violet-200 ring-1 ring-violet-400/30",
     accentBar: "before:bg-violet-500/40",
-    headerText: "text-violet-200",
+    headerText: "text-violet-800 dark:text-violet-200",
   },
   orchestrator: {
     label: "Main agent",
     icon: Workflow,
     avatarRing:
-      "bg-gradient-to-br from-teal-500/30 to-status-success/20 text-teal-200 ring-1 ring-teal-400/30",
+      "bg-gradient-to-br from-teal-500/30 to-status-success/20 text-teal-800 dark:text-teal-200 ring-1 ring-teal-400/30",
     accentBar: "before:bg-teal-500/40",
-    headerText: "text-teal-200",
+    headerText: "text-teal-800 dark:text-teal-200",
   },
   system: {
     label: "System",
@@ -169,7 +169,7 @@ function SessionEventRow({ title, timestamp }: { title?: string; timestamp: stri
   return (
     <div className="flex items-center justify-center py-1">
       <div className="inline-flex items-center gap-2 text-[11px] text-fg-secondary bg-surface-2/70 border border-surface-3 rounded-full px-3 py-1 max-w-full">
-        <Pencil className="w-3 h-3 text-violet-300/70 flex-shrink-0" />
+        <Pencil className="w-3 h-3 text-violet-700/70 dark:text-violet-300/70 flex-shrink-0" />
         <span className="text-fg-muted">Renamed session →</span>
         <span className="text-fg-secondary font-medium truncate">{title || "(untitled)"}</span>
         {timestamp && (
@@ -253,11 +253,13 @@ function renderSegment(seg: TuiSegment, key: number): React.ReactNode {
         <CollapsibleBlock
           key={key}
           text={seg.text}
-          icon={<ScrollText className="w-3.5 h-3.5 text-violet-400/60 flex-shrink-0" />}
+          icon={
+            <ScrollText className="w-3.5 h-3.5 text-violet-700/60 dark:text-violet-400/60 flex-shrink-0" />
+          }
           title="Persisted output"
           borderClass="border-violet-500/20"
           bgClass="bg-violet-500/5"
-          textClass="text-violet-300/80"
+          textClass="text-violet-700/80 dark:text-violet-300/80"
         />
       );
     case "text": {
@@ -394,7 +396,9 @@ export function MessageList({ messages, loading }: MessageListProps) {
                   <span className="text-[10px] text-fg-muted font-mono inline-flex items-center gap-1">
                     <span className="text-status-success/70">↓ {fmt(msg.usage.input_tokens)}</span>
                     <span className="text-fg-muted">·</span>
-                    <span className="text-orange-300/70">↑ {fmt(msg.usage.output_tokens)}</span>
+                    <span className="text-orange-700/70 dark:text-orange-300/70">
+                      ↑ {fmt(msg.usage.output_tokens)}
+                    </span>
                   </span>
                 )}
                 {msg.timestamp && (
@@ -413,11 +417,13 @@ export function MessageList({ messages, loading }: MessageListProps) {
                       <CollapsibleBlock
                         key={bIdx}
                         text={block.text}
-                        icon={<ScrollText className="w-3.5 h-3.5 text-cyan-400/60 flex-shrink-0" />}
+                        icon={
+                          <ScrollText className="w-3.5 h-3.5 text-cyan-700/60 dark:text-cyan-400/60 flex-shrink-0" />
+                        }
                         title="Task Notification"
                         borderClass="border-cyan-500/20"
                         bgClass="bg-cyan-500/5"
-                        textClass="text-cyan-400/80"
+                        textClass="text-cyan-700/80 dark:text-cyan-400/80"
                       />
                     );
                   }