Refactor WASM REPL into host-driven stdio runtime with streaming interrupts

[Copilot]

This change pivots the web/WASM path from browser-specific JSFFI callbacks to a decoupled, host-mediated runtime model. The same impli.wasm now runs as a stdio-driven REPL (e.g. in Wasmtime) while the browser frontend acts as an input/output host, including streaming interrupt signaling and read x wait semantics.

• Runtime contract shift (WASM as decoupled backend)

  • Removed browser-coupled JSFFI control flow from the WASM entry path.
  • Reworked the WASM executable to run as a stdio-driven REPL process model rather than a browser-bound reactor export surface.

• Host input broker + control messages

  • Added a stdin router in Web.hs that:
    • forwards normal lines to the REPL input queue,
    • treats :interrupt / \ETX as out-of-band control messages,
    • preserves blocking read behavior for read x by waiting on queued input.

• Asynchronous interrupt plumbing in interpreter semantics

  • Introduced global interrupt primitives in IMP.State (requestInterrupt, consumeInterrupt).
  • Integrated interrupt polling into While execution in both natural and structural semantics, allowing long-running loops to be interrupted by streamed host control messages.

• Browser frontend as stdio host

  • Reworked web/src/impli.ts to mediate stdin/stdout/stderr through @runno/wasi instead of global impli.* JSFFI methods.
  • Added byte-queue based stdin feeding, Ctrl-C mapping to :interrupt, and continued terminal-driven line input handling.

• Build/docs alignment

  • Updated cabal config for the new WASM runtime shape (including stm dependency).
  • Updated web architecture docs to describe stdio mediation and removed obsolete stub import usage.

this.terminal.attachCustomKeyEventHandler((event) => {
  if (event.type === "keydown" && event.ctrlKey && event.key.toLowerCase() === "c") {
    this.enqueueLine(":interrupt");
    this.write("^C\r\n");
    return false;
  }
  return true;
});