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/examples/extensions/timed-confirm.ts

@@ -1,70 +0,0 @@
-/**
- * Example extension demonstrating timed dialogs with live countdown.
- *
- * Commands:
- * - /timed - Shows confirm dialog that auto-cancels after 5 seconds with countdown
- * - /timed-select - Shows select dialog that auto-cancels after 10 seconds with countdown
- * - /timed-signal - Shows confirm using AbortSignal (manual approach)
- */
-
-import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
-
-export default function (pi: ExtensionAPI) {
-	// Simple approach: use timeout option (recommended)
-	pi.registerCommand("timed", {
-		description: "Show a timed confirmation dialog (auto-cancels in 5s with countdown)",
-		handler: async (_args, ctx) => {
-			const confirmed = await ctx.ui.confirm(
-				"Timed Confirmation",
-				"This dialog will auto-cancel in 5 seconds. Confirm?",
-				{ timeout: 5000 },
-			);
-
-			if (confirmed) {
-				ctx.ui.notify("Confirmed by user!", "info");
-			} else {
-				ctx.ui.notify("Cancelled or timed out", "info");
-			}
-		},
-	});
-
-	pi.registerCommand("timed-select", {
-		description: "Show a timed select dialog (auto-cancels in 10s with countdown)",
-		handler: async (_args, ctx) => {
-			const choice = await ctx.ui.select("Pick an option", ["Option A", "Option B", "Option C"], { timeout: 10000 });
-
-			if (choice) {
-				ctx.ui.notify(`Selected: ${choice}`, "info");
-			} else {
-				ctx.ui.notify("Selection cancelled or timed out", "info");
-			}
-		},
-	});
-
-	// Manual approach: use AbortSignal for more control
-	pi.registerCommand("timed-signal", {
-		description: "Show a timed confirm using AbortSignal (manual approach)",
-		handler: async (_args, ctx) => {
-			const controller = new AbortController();
-			const timeoutId = setTimeout(() => controller.abort(), 5000);
-
-			ctx.ui.notify("Dialog will auto-cancel in 5 seconds...", "info");
-
-			const confirmed = await ctx.ui.confirm(
-				"Timed Confirmation",
-				"This dialog will auto-cancel in 5 seconds. Confirm?",
-				{ signal: controller.signal },
-			);
-
-			clearTimeout(timeoutId);
-
-			if (confirmed) {
-				ctx.ui.notify("Confirmed by user!", "info");
-			} else if (controller.signal.aborted) {
-				ctx.ui.notify("Dialog timed out (auto-cancelled)", "warning");
-			} else {
-				ctx.ui.notify("Cancelled by user", "info");
-			}
-		},
-	});
-}