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/ai/test/google-gemini-cli-retry-delay.test.ts

@@ -1,53 +0,0 @@
-import { afterEach, describe, expect, it, vi } from "vitest";
-import { extractRetryDelay } from "../src/providers/google-gemini-cli.js";
-
-describe("extractRetryDelay header parsing", () => {
-	afterEach(() => {
-		vi.useRealTimers();
-	});
-
-	it("prefers Retry-After seconds header", () => {
-		vi.useFakeTimers();
-		vi.setSystemTime(new Date("2025-01-01T00:00:00Z"));
-
-		const response = new Response("", { headers: { "Retry-After": "5" } });
-		const delay = extractRetryDelay("Please retry in 1s", response);
-
-		expect(delay).toBe(6000);
-	});
-
-	it("parses Retry-After HTTP date header", () => {
-		vi.useFakeTimers();
-		const now = new Date("2025-01-01T00:00:00Z");
-		vi.setSystemTime(now);
-
-		const retryAt = new Date(now.getTime() + 12000).toUTCString();
-		const response = new Response("", { headers: { "Retry-After": retryAt } });
-		const delay = extractRetryDelay("", response);
-
-		expect(delay).toBe(13000);
-	});
-
-	it("parses x-ratelimit-reset header", () => {
-		vi.useFakeTimers();
-		const now = new Date("2025-01-01T00:00:00Z");
-		vi.setSystemTime(now);
-
-		const resetAtMs = now.getTime() + 20000;
-		const resetSeconds = Math.floor(resetAtMs / 1000).toString();
-		const response = new Response("", { headers: { "x-ratelimit-reset": resetSeconds } });
-		const delay = extractRetryDelay("", response);
-
-		expect(delay).toBe(21000);
-	});
-
-	it("parses x-ratelimit-reset-after header", () => {
-		vi.useFakeTimers();
-		vi.setSystemTime(new Date("2025-01-01T00:00:00Z"));
-
-		const response = new Response("", { headers: { "x-ratelimit-reset-after": "30" } });
-		const delay = extractRetryDelay("", response);
-
-		expect(delay).toBe(31000);
-	});
-});