chore: drop non-code junk (pi-mono-reference, runtime state, root duplicates)

Remove files that should never have been tracked:

- pi-mono-reference/: 688-file copy of an upstream monorepo, zero imports,
  used only as offline human reference
- build/electron-builder.runtime.json: environment-specific build artifact
  with hardcoded local paths
- state/cancel-signal-state.json: runtime state written by the app
- prompt.txt, logo.svg (root): exact duplicates of the canonical copies
  under .planning/archive/ and assets/

Add state/ to .gitignore so future runtime state stays out.

pi-mono-reference/packages/coding-agent/src/core/exec.ts

@@ -1,107 +0,0 @@
-/**
- * Shared command execution utilities for extensions and custom tools.
- */
-
-import { spawn } from "node:child_process";
-import { waitForChildProcess } from "../utils/child-process.js";
-
-/**
- * Options for executing shell commands.
- */
-export interface ExecOptions {
-	/** AbortSignal to cancel the command */
-	signal?: AbortSignal;
-	/** Timeout in milliseconds */
-	timeout?: number;
-	/** Working directory */
-	cwd?: string;
-}
-
-/**
- * Result of executing a shell command.
- */
-export interface ExecResult {
-	stdout: string;
-	stderr: string;
-	code: number;
-	killed: boolean;
-}
-
-/**
- * Execute a shell command and return stdout/stderr/code.
- * Supports timeout and abort signal.
- */
-export async function execCommand(
-	command: string,
-	args: string[],
-	cwd: string,
-	options?: ExecOptions,
-): Promise<ExecResult> {
-	return new Promise((resolve) => {
-		const proc = spawn(command, args, {
-			cwd,
-			shell: false,
-			stdio: ["ignore", "pipe", "pipe"],
-		});
-
-		let stdout = "";
-		let stderr = "";
-		let killed = false;
-		let timeoutId: NodeJS.Timeout | undefined;
-
-		const killProcess = () => {
-			if (!killed) {
-				killed = true;
-				proc.kill("SIGTERM");
-				// Force kill after 5 seconds if SIGTERM doesn't work
-				setTimeout(() => {
-					if (!proc.killed) {
-						proc.kill("SIGKILL");
-					}
-				}, 5000);
-			}
-		};
-
-		// Handle abort signal
-		if (options?.signal) {
-			if (options.signal.aborted) {
-				killProcess();
-			} else {
-				options.signal.addEventListener("abort", killProcess, { once: true });
-			}
-		}
-
-		// Handle timeout
-		if (options?.timeout && options.timeout > 0) {
-			timeoutId = setTimeout(() => {
-				killProcess();
-			}, options.timeout);
-		}
-
-		proc.stdout?.on("data", (data) => {
-			stdout += data.toString();
-		});
-
-		proc.stderr?.on("data", (data) => {
-			stderr += data.toString();
-		});
-
-		// Wait for process termination without hanging on inherited stdio handles
-		// held open by detached descendants.
-		waitForChildProcess(proc)
-			.then((code) => {
-				if (timeoutId) clearTimeout(timeoutId);
-				if (options?.signal) {
-					options.signal.removeEventListener("abort", killProcess);
-				}
-				resolve({ stdout, stderr, code: code ?? 0, killed });
-			})
-			.catch((_err) => {
-				if (timeoutId) clearTimeout(timeoutId);
-				if (options?.signal) {
-					options.signal.removeEventListener("abort", killProcess);
-				}
-				resolve({ stdout, stderr, code: 1, killed });
-			});
-	});
-}