Add starter prompt suggestions to the empty conversation state

[DragonnZhang]

Closes #72

What & why

A new conversation shows a centered composer under "What should we build?" and nothing else. Every comparable desktop client (Claude Code Desktop "prompt suggestions", ChatGPT / Codex example prompts) fills that blank canvas with clickable starting points. This adds the same to OpenWork.

What changed

• EmptyStateSuggestions (new, apps/electron/src/renderer/components/app-shell/EmptyStateSuggestions.tsx) — a row of 4 build-oriented suggestion chips (Explain this codebase, Build a feature, Fix a bug, Write tests), each a localized label + icon.
• ChatDisplay — renders the chips beneath the centered empty-state composer, only while the composer is empty. Clicking a chip seeds the composer with the fuller localized prompt through the existing controlled-draft channel (onInputChange → inputValue) and focuses the input. It does not auto-send — the user can edit first. Chips disappear once the composer has content (seeded or typed).
• i18n — 8 new keys (chat.suggestions.<id>.title / .prompt) added to all 7 locales.
• e2e — e2e/assertions/starter-suggestions.assert.ts driving the full path.

Frontend-only: no backend / qwen-code changes, no new IPC, no new persistence — content is static and localized, seeding reuses the path drafts already use.

Verification

Check	Result
bun run typecheck:all	✅ zero delta vs main (11 pre-existing electron-typecheck baseline errors — missing vitest types + an auto-update.ts type issue — byte-identical with/without this change; packages/ui clean)
bun test	✅ zero delta vs main (56 pre-existing baseline failures byte-identical with/without this change)
bun run electron:build:renderer	✅ builds
bun run lint:i18n:parity	✅ 6 locales, 1552 keys each
eslint (touched files)	✅ 0 errors
CDP assertion (bun run e2e)	⚠️ could not execute in this environment — the Electron binary can't be installed (its download host github.com/releases returns 403 under the sandbox egress policy; node_modules/electron/dist/electron is absent). The assertion is included and transpile-checked so it runs in CI / locally where Electron is available.

CDP assertion coverage

The assertion drives the real UI end-to-end (not "it booted"):

1. Reaches the ready AppShell and waits for [data-testid="empty-suggestions"].
2. Asserts 4 visible chips.
3. Asserts the composer starts empty.
4. Clicks the first chip and asserts the composer is populated with a prompt longer than the chip's short label (proving it seeds the prompt, not the title).
5. Asserts the suggestions surface disappears once the composer has content.

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