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/utils/clipboard.ts

@@ -1,81 +0,0 @@
-import { execSync, spawn } from "child_process";
-import { platform } from "os";
-import { isWaylandSession } from "./clipboard-image.js";
-import { clipboard } from "./clipboard-native.js";
-
-type NativeClipboardExecOptions = {
-	input: string;
-	timeout: number;
-	stdio: ["pipe", "ignore", "ignore"];
-};
-
-function copyToX11Clipboard(options: NativeClipboardExecOptions): void {
-	try {
-		execSync("xclip -selection clipboard", options);
-	} catch {
-		execSync("xsel --clipboard --input", options);
-	}
-}
-
-export async function copyToClipboard(text: string): Promise<void> {
-	// Always emit OSC 52 - works over SSH/mosh, harmless locally
-	const encoded = Buffer.from(text).toString("base64");
-	process.stdout.write(`\x1b]52;c;${encoded}\x07`);
-
-	try {
-		if (clipboard) {
-			await clipboard.setText(text);
-			return;
-		}
-	} catch {
-		// Fall through to platform-specific clipboard tools.
-	}
-
-	// Also try native tools (best effort for local sessions)
-	const p = platform();
-	const options: NativeClipboardExecOptions = { input: text, timeout: 5000, stdio: ["pipe", "ignore", "ignore"] };
-
-	try {
-		if (p === "darwin") {
-			execSync("pbcopy", options);
-		} else if (p === "win32") {
-			execSync("clip", options);
-		} else {
-			// Linux. Try Termux, Wayland, or X11 clipboard tools.
-			if (process.env.TERMUX_VERSION) {
-				try {
-					execSync("termux-clipboard-set", options);
-					return;
-				} catch {
-					// Fall back to Wayland or X11 tools.
-				}
-			}
-
-			const hasWaylandDisplay = Boolean(process.env.WAYLAND_DISPLAY);
-			const hasX11Display = Boolean(process.env.DISPLAY);
-			const isWayland = isWaylandSession();
-			if (isWayland && hasWaylandDisplay) {
-				try {
-					// Verify wl-copy exists (spawn errors are async and won't be caught)
-					execSync("which wl-copy", { stdio: "ignore" });
-					// wl-copy with execSync hangs due to fork behavior; use spawn instead
-					const proc = spawn("wl-copy", [], { stdio: ["pipe", "ignore", "ignore"] });
-					proc.stdin.on("error", () => {
-						// Ignore EPIPE errors if wl-copy exits early
-					});
-					proc.stdin.write(text);
-					proc.stdin.end();
-					proc.unref();
-				} catch {
-					if (hasX11Display) {
-						copyToX11Clipboard(options);
-					}
-				}
-			} else if (hasX11Display) {
-				copyToX11Clipboard(options);
-			}
-		}
-	} catch {
-		// Ignore - OSC 52 already emitted as fallback
-	}
-}