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/web-ui/src/utils/auth-token.ts

@@ -1,22 +0,0 @@
-import PromptDialog from "@mariozechner/mini-lit/dist/PromptDialog.js";
-import { i18n } from "./i18n.js";
-
-export async function getAuthToken(): Promise<string | undefined> {
-	let authToken: string | undefined = localStorage.getItem(`auth-token`) || "";
-	if (authToken) return authToken;
-
-	while (true) {
-		authToken = (
-			await PromptDialog.ask(i18n("Enter Auth Token"), i18n("Please enter your auth token."), "", true)
-		)?.trim();
-		if (authToken) {
-			localStorage.setItem(`auth-token`, authToken);
-			break;
-		}
-	}
-	return authToken?.trim() || undefined;
-}
-
-export async function clearAuthToken() {
-	localStorage.removeItem(`auth-token`);
-}