AD-1104: Add runnable web app

[alph-cmky]

Summary

• Replace the placeholder web dev script with a real Next.js dev server.
• Add Next/React dependencies, Next config, root layout, and generated Next env types.
• Render the existing app shell, runtime dashboard, and workflow canvas on the browser home page.
• Add a focused home page smoke test for the MVP surface.
• Add runtime dashboard styles and ignore Next build output in git/eslint.
• Update the AD-1104 backlog checklist.

Browser smoke

• Started pnpm --filter @agentdeck/web dev --hostname 127.0.0.1 --port 3100.
• Verified http://127.0.0.1:3100/ rendered AgentDeck, OpenAI Codex CLI, and Review Flow in the browser DOM.
• Screenshot capture timed out twice in the browser tool, so DOM smoke results are recorded here instead.

Testing

• TDD red check: pnpm test apps/web/src/app/page.test.ts initially failed because renderHomePageHtml did not exist.
• pnpm test apps/web/src/app/page.test.ts
• pnpm --filter @agentdeck/web build
• pnpm lint && pnpm format && pnpm typecheck && pnpm test && pnpm build

Stacked on #53.