refactor: move MiniApp host plans and developer tooling

[limityan]

Summary

• Move MiniApp fs.* and shell.exec host call planning into bitfun-product-domains while keeping permission-sensitive execution in core.
• Keep bitfun-core as the executor for permission policy resolution, canonicalized path checks, file IO, process spawning, net.fetch, and os.info runtime behavior.
• Streamline root contributor and agent guidance by moving DeepReview-specific rules to local AGENTS.md files and simplifying Windows OpenSSL setup notes.
• Make desktop DevTools shortcuts more reliable with F12 for native DevTools and a backend availability guard so final release builds do not register debug shortcuts.

Risk / behavior

• No MiniApp tool schema, permission semantics, storage layout, worker lifecycle, or release-shape changes are intended.
• net.fetch, os.info, worker execution, seed/marker IO, and function-agent AI provider acquisition remain in core to avoid new runtime dependencies or behavior drift.
• Product Domains adds no new third-party/runtime dependencies.
• Desktop DevTools shortcuts are limited to debug/devtools-enabled desktop builds; release stubs report unavailable and the frontend does not intercept the shortcuts.
• Documentation changes reduce root-level module detail and do not alter product logic.

Refs #970

Verification

• cargo test -p bitfun-product-domains --features product-full
• cargo test -p bitfun-harness
• cargo test -p bitfun-core miniapp::host_dispatch -- --nocapture
• node scripts/check-core-boundaries.mjs
• node scripts/core-boundaries/self-test.mjs
• pnpm run fmt:rs
• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run src/infrastructure/debug/useDebugInspector.test.tsx
• cargo check -p bitfun-desktop
• pnpm run check:repo-hygiene
• cargo check --workspace
• git diff --check