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/SessionOverview.tsx

@@ -95,21 +95,21 @@ function StatTile({
 }) {
   const palette = {
     default: "border-surface-3 bg-surface-2 text-fg-secondary",
-    violet: "border-violet-500/20 bg-violet-500/5 text-violet-200",
+    violet: "border-violet-500/20 bg-violet-500/5 text-violet-800 dark:text-violet-200",
     emerald: "border-status-success/20 bg-status-success/5 text-status-success",
     amber: "border-status-warning/20 bg-status-warning/5 text-status-warning",
-    rose: "border-rose-500/20 bg-rose-500/5 text-rose-200",
-    cyan: "border-cyan-500/20 bg-cyan-500/5 text-cyan-200",
-    blue: "border-blue-600/20 bg-blue-600/5 text-blue-300",
+    rose: "border-rose-500/20 bg-rose-500/5 text-rose-800 dark:text-rose-200",
+    cyan: "border-cyan-500/20 bg-cyan-500/5 text-cyan-800 dark:text-cyan-200",
+    blue: "border-blue-600/20 bg-blue-600/5 text-blue-700 dark:text-blue-300",
   }[tone];
 
   const iconTone = {
     default: "text-fg-muted",
-    violet: "text-violet-400",
+    violet: "text-violet-700 dark:text-violet-400",
     emerald: "text-status-success",
     amber: "text-status-warning",
-    rose: "text-rose-400",
-    cyan: "text-cyan-400",
+    rose: "text-rose-700 dark:text-rose-400",
+    cyan: "text-cyan-700 dark:text-cyan-400",
     blue: "text-blue-500",
   }[tone];
 
@@ -359,7 +359,7 @@ export function SessionOverview({ session, agents }: SessionOverviewProps) {
         <div className="lg:col-span-2 rounded-lg border border-surface-3 bg-surface-2/60 p-3.5">
           <div className="flex items-center justify-between mb-3">
             <h3 className="text-xs font-semibold text-fg-secondary uppercase tracking-wider flex items-center gap-1.5">
-              <Wrench className="w-3.5 h-3.5 text-violet-400" />
+              <Wrench className="w-3.5 h-3.5 text-violet-700 dark:text-violet-400" />
               Top tools
             </h3>
             <span className="text-[10px] text-fg-muted font-mono">
@@ -418,7 +418,7 @@ export function SessionOverview({ session, agents }: SessionOverviewProps) {
               <>
                 <div className="flex items-center justify-between mb-3">
                   <h3 className="text-xs font-semibold text-fg-secondary uppercase tracking-wider flex items-center gap-1.5">
-                    <GitBranch className="w-3.5 h-3.5 text-cyan-400" />
+                    <GitBranch className="w-3.5 h-3.5 text-cyan-700 dark:text-cyan-400" />
                     Subagents
                   </h3>
                   <span className="text-[10px] text-fg-muted font-mono">{totalRuns} runs</span>
@@ -508,14 +508,14 @@ function TokenFlowBar({ tokens, total }: { tokens: SessionStats["tokens"]; total
       label: "Cache read",
       value: tokens.cache_read_tokens,
       cls: "bg-sky-500",
-      text: "text-sky-300",
+      text: "text-sky-700 dark:text-sky-300",
     },
     {
       key: "cache_write",
       label: "Cache write",
       value: tokens.cache_write_tokens,
       cls: "bg-violet-500",
-      text: "text-violet-300",
+      text: "text-violet-700 dark:text-violet-300",
     },
     {
       key: "input",
@@ -529,7 +529,7 @@ function TokenFlowBar({ tokens, total }: { tokens: SessionStats["tokens"]; total
       label: "Output",
       value: tokens.output_tokens,
       cls: "bg-orange-500",
-      text: "text-orange-300",
+      text: "text-orange-700 dark:text-orange-300",
     },
   ];