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/cli/config-selector.ts

@@ -1,52 +0,0 @@
-/**
- * TUI config selector for `pi config` command
- */
-
-import { ProcessTerminal, TUI } from "@mariozechner/pi-tui";
-import type { ResolvedPaths } from "../core/package-manager.js";
-import type { SettingsManager } from "../core/settings-manager.js";
-import { ConfigSelectorComponent } from "../modes/interactive/components/config-selector.js";
-import { initTheme, stopThemeWatcher } from "../modes/interactive/theme/theme.js";
-
-export interface ConfigSelectorOptions {
-	resolvedPaths: ResolvedPaths;
-	settingsManager: SettingsManager;
-	cwd: string;
-	agentDir: string;
-}
-
-/** Show TUI config selector and return when closed */
-export async function selectConfig(options: ConfigSelectorOptions): Promise<void> {
-	// Initialize theme before showing TUI
-	initTheme(options.settingsManager.getTheme(), true);
-
-	return new Promise((resolve) => {
-		const ui = new TUI(new ProcessTerminal());
-		let resolved = false;
-
-		const selector = new ConfigSelectorComponent(
-			options.resolvedPaths,
-			options.settingsManager,
-			options.cwd,
-			options.agentDir,
-			() => {
-				if (!resolved) {
-					resolved = true;
-					ui.stop();
-					stopThemeWatcher();
-					resolve();
-				}
-			},
-			() => {
-				ui.stop();
-				stopThemeWatcher();
-				process.exit(0);
-			},
-			() => ui.requestRender(),
-		);
-
-		ui.addChild(selector);
-		ui.setFocus(selector.getResourceList());
-		ui.start();
-	});
-}