feat(tui): detect terminal color scheme and apply light-optimised palette

Squash of the linearized fix/tui-color-scheme-v2 merge and the follow-up
catalog regeneration. Renders error cause chains at every diagnostic seam
(origin/fetch-failed-diagnostics) and adds color scheme detection with a
light-terminal palette.

packages/context/workspace-context/src/index.ts

@@ -92,7 +92,6 @@ export function apply(ctx: Context, config: Config): void {
     if (update !== undefined) {
       agent.inject(update.context.content, {
         source: update.context.source,
-        envelope: update.context.envelope,
         meta: update.context.meta,
       })
       applyInstructionVersionUpdates(agent.session, update.versionUpdates, instructionVersions)