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/MarkdownContent.tsx

@@ -320,7 +320,7 @@ function renderInline(text: string, baseKey = ""): React.ReactNode[] {
           href={linkM[2]!}
           target="_blank"
           rel="noopener noreferrer"
-          className="text-violet-300 hover:text-violet-200 underline underline-offset-2 decoration-violet-400/40 hover:decoration-violet-300/70"
+          className="text-violet-700 dark:text-violet-300 hover:text-violet-800 dark:hover:text-violet-200 underline underline-offset-2 decoration-violet-400/40 hover:decoration-violet-300/70"
         >
           {renderInline(linkM[1]!, `${baseKey}-l${n}`)}
         </a>
@@ -337,7 +337,7 @@ function renderInline(text: string, baseKey = ""): React.ReactNode[] {
           href={urlM[0]}
           target="_blank"
           rel="noopener noreferrer"
-          className="text-violet-300 hover:text-violet-200 underline underline-offset-2 decoration-violet-400/40 hover:decoration-violet-300/70 break-all"
+          className="text-violet-700 dark:text-violet-300 hover:text-violet-800 dark:hover:text-violet-200 underline underline-offset-2 decoration-violet-400/40 hover:decoration-violet-300/70 break-all"
         >
           {urlM[0]}
         </a>
@@ -428,7 +428,10 @@ export function MarkdownContent({ text, dense = false }: MarkdownContentProps) {
               );
             }
             return (
-              <ul key={idx} className="list-disc pl-5 space-y-1 marker:text-violet-400/60">
+              <ul
+                key={idx}
+                className="list-disc pl-5 space-y-1 marker:text-violet-700/60 dark:marker:text-violet-400/60"
+              >
                 {b.items.map((item, i) => (
                   <li key={i} className="text-sm text-fg-secondary">
                     {renderListItem(item, `li${idx}-${i}`)}