feat(jupyter): rewrite kernel in JS, drop zeromq/runtimelib deps

[lunadogbot]

Summary

Replaces the Rust-based ZMQ kernel implementation (using zeromq, runtimelib/jupyter_runtime, and jupyter-protocol crates) with a pure-JS ZMTP 3.1 implementation running on top of Deno.listen().

Architecture

• Main OS thread — new cli/js/jupyter_kernel.js (~800 lines) owns all ZMQ/Jupyter protocol work: ZMTP 3.1 framing, NULL handshake, HMAC-SHA256 message signing, and all five channel loops (shell, control, iopub, heartbeat, stdin). Uses only non-blocking Deno.listen() TCP, so the event loop never blocks.
• Background OS thread — runs the REPL session (user code evaluation, CDP, TypeScript). Created via a cloned CliMainWorkerFactory.
• The two threads talk over tokio::mpsc channels. The main thread can interrupt user code at any time by calling IsolateHandle::terminate_execution() on the handle sent back from the background thread via a oneshot channel.

Changes

• cli/js/jupyter_kernel.js — new JS file: ZMTP framing helpers, NULL handshake, Jupyter wire protocol (HMAC-SHA256 via crypto.subtle), RouterSocket/PubSocket server classes, startJupyterKernel() entry point
• cli/ops/jupyter.rs — rewritten: deno_jupyter_kernel extension (get_connection_info, repl_evaluate, recv_iopub, interrupt, etc.) and deno_jupyter_repl extension (broadcast, print, create_png, get_buffer)
• cli/tools/jupyter/mod.rs — new two-thread orchestration; REPL background thread sends isolate handle via oneshot so the kernel thread can interrupt it
• cli/tools/jupyter/server.rs — deleted (all Rust ZMQ code gone)
• cli/tools/jupyter/install.rs — replace jupyter_runtime::dirs with platform-specific path logic (XDG on Linux, ~/Library on macOS, %APPDATA% on Windows)
• cli/lib/worker.rs, cli/worker.rs — #[derive(Clone)] on worker factories so one factory can create workers on two threads
• cli/cdp.rs — add missing Serialize/Deserialize derives needed by new ops
• cli/js/40_jupyter.js — update enableJupyter() for new op signatures
• runtime/js/99_main.js — update NOT_IMPORTED_OPS for new kernel ops
• tests/integration/jupyter_client.rs — new pure-Rust ZMTP 3.1 test client (ReqSocket, DealerSocket, SubSocket, RouterSocket) replacing the zeromq crate dependency
• tests/integration/jupyter_tests.rs — rewritten to use the new in-tree client
• Cargo.toml / cli/Cargo.toml / tests/integration/Cargo.toml — remove zeromq, runtimelib, jupyter-protocol dependencies

Test plan

• cargo check -p deno passes with no errors
• cargo check --manifest-path tests/integration/Cargo.toml passes
• cargo test jupyter — integration tests for heartbeat, kernel_info, execute_request, interrupt, shutdown, HTTP server
• deno jupyter --install registers the kernel correctly on each platform
• Manual: jupyter console --kernel deno connects and evaluates code

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