fix(agent): enforce non-app surface boundaries

[iamjr15]

Why

Explicit Documents, Slides, Data, Research, and Media selections were preserved as request metadata, but the projectless app fallback and model tool registry still treated them as general app-capable runs. A document request whose subject mentioned a website could therefore scaffold and preview an unrelated Next.js app.

What changed

• short-circuit projectless app inference whenever an explicit non-app run intent is present
• resolve exact per-surface model tool allowlists while keeping app-builder topology authoritative
• advertise only surface-relevant bundled and custom skills
• make the selected artifact outcome explicit in the run prompt without mutating visible user text
• auto-select Browser only for hydrated web/mobile app project modes; Files remains authoritative for non-app work
• document the execution and Computer-surface contracts

Verification

• pnpm lint
• pnpm typecheck
• pnpm turbo build --force
• pnpm deadcode
• pnpm architecture:check
• pnpm turbo skills:build
• policy probe confirmed Documents, Slides, Data, Research, and Media profiles expose no browser, dev-server, or git tools

Production browser QA will run after the exact commit is merged and deployed to Vercel and Cloudflare.