feat(net): add bounded fetch(net) module

[siwei-yuan]

Summary

• add a spec-pinned globalThis.net module and framework-neutral fetch() SDK
• add the transport-neutral pocket-net Rust core with bounded handles, tick-batched completions, response ownership, portable errors, and a host-owned HttpTransport seam
• add deterministic sim and browser-fetch host adapters, lazy service pumping across Solid/Vue Vapor/Octane, capability/export codegen, tests, and docs

Design

NET v1 is intentionally a bounded whole-response HTTP client rather than a complete WHATWG Fetch implementation. It supports common app methods, headers, string/byte bodies, timeout and per-request maxBytes; it omits streams, cookies, cache, Request/Headers, AbortSignal, WebSocket, servers, and raw sockets.

Concrete DNS/TLS/HTTP libraries remain host-owned. pocket-net does not depend on ureq, reqwest, ESP-IDF, or a runtime executor; downstream hosts implement HttpTransport::start/cancel/drain. Network workers never call QuickJS, and the guest polls once per tick only while requests are pending. One poll drains the complete visible batch.

Verification

• bun run test — 11/11 stages green
• bunx tsc --noEmit
• cargo test -p pocket-net --manifest-path engine/Cargo.toml — 5 passed
• cargo clippy -p pocket-net --all-targets --manifest-path engine/Cargo.toml -- -D warnings
• cargo check --workspace --manifest-path engine/Cargo.toml
• bun run site:build
• bun tests/contract.ts