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/config/ScopeBadge.tsx

@@ -12,11 +12,11 @@ export function ScopeBadge({ scope }: { scope: string }) {
   const { t } = useTranslation("ccConfig");
   const color =
     scope === "user"
-      ? "bg-sky-500/10 text-sky-300 border-sky-500/30"
+      ? "bg-sky-500/10 text-sky-700 dark:text-sky-300 border-sky-500/30"
       : scope === "project"
         ? "bg-status-success/10 text-status-success border-status-success/30"
         : scope === "project-local"
-          ? "bg-violet-500/10 text-violet-300 border-violet-500/30"
+          ? "bg-violet-500/10 text-violet-700 dark:text-violet-300 border-violet-500/30"
           : "bg-surface-3 text-fg-secondary border-border";
   const label =
     scope === "project-local"