fix(app): render code blocks with theme-aware Shiki palette

[magic-peach]

Summary

• Code blocks in assistant messages (and artifact/extension markdown) were always highlighted with Shiki's github-light theme, so tokens were unreadable in dark mode.
• Switched codeToHtml to dual themes (themes: { light: "github-light", dark: "github-dark" }, defaultColor: "light"), which emits the dark palette as --shiki-dark* CSS variables alongside the unchanged light colors.
• Added a small CSS rule in src/app/index.css that activates the dark variables under .dark / [data-theme="dark"] (matching the app's existing dark variant selectors).

Why

• Fixes low-contrast/unreadable code in dark mode. The dual-theme approach also means code blocks flip instantly when the user switches theme — no re-parse or re-highlight needed, unlike checking the DOM theme at highlight time (the app sets data-theme on the root, not a dark class, so the snippet suggested in the issue would not have matched).

Issue

• Closes Code block dark mode bug - Shiki theme hardcoded to github-light #2440

Scope

• apps/app/src/components/markdown/markdown.tsx (chat message renderer, the file cited in the issue)
• apps/app/src/react-app/domains/session/surface/markdown.tsx (artifact preview / extension detail renderer — identical hardcoded theme, same 2-line fix)
• apps/app/src/app/index.css (one CSS rule to activate the dark palette)

Out of scope

• src/components/ui/code-block.tsx (already takes theme as a prop; callers can opt in separately)
• Any change to light-mode rendering — the light palette is still emitted inline exactly as before.

Testing

Ran

• pnpm install
• pnpm --filter @openwork/app typecheck

Result

• pass/fail: pass (no type errors)

CI status

• pass: Vercel Preview Comments, Vercel openwork-landing
• code-related failures: none
• external/env/auth blockers: the three "Vercel – openwork-app / openwork-den / openwork-den-worker-proxy" checks fail with "Authorization required to deploy" — a fork-deploy authorization gate, unrelated to this change (which only touches the Electron app's renderer, not any Vercel-deployed app).

Manual verification

1. Rendered real output through the repo's own shiki@4 with the new options and confirmed the HTML contains both the inline light colors and --shiki-dark / --shiki-dark-bg variables.
2. Loaded that output in a page with the new CSS rule and captured light vs dark side by side (screenshot below).
3. In-app repro for reviewers: Settings > Appearance > Dark, send a message containing a fenced code block, confirm tokens use the github-dark palette; switch back to Light and confirm rendering is unchanged.

Evidence

Left: light theme after the fix (unchanged). Right top: current dark-mode bug (light palette on dark background). Right bottom: dark theme after the fix.

I was not able to capture an in-app video for this one — the verification above was done against the real Shiki pipeline and CSS outside Electron; the 3-step in-app repro is listed for the reviewer.

Risk

• Low. Light mode output is byte-identical apart from added CSS variables; the dark override is scoped to .shiki elements under the dark theme selectors.

Rollback

• Revert this commit; no data or config migrations involved.

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Project	Deployment	Actions	Updated (UTC)
openwork-landing	Ready	Preview, Comment, Open in v0	Jul 3, 2026 6:39pm

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[magic-peach]

@benjaminshafii could you please review my pr?