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/test/image-resize-callers.test.ts

@@ -1,53 +0,0 @@
-import { mkdirSync, rmSync, writeFileSync } from "node:fs";
-import { tmpdir } from "node:os";
-import { join } from "node:path";
-import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-
-vi.mock("../src/utils/image-resize.js", () => ({
-	resizeImage: vi.fn(),
-	formatDimensionNote: vi.fn(() => undefined),
-}));
-
-import { processFileArguments } from "../src/cli/file-processor.js";
-import { createReadTool } from "../src/core/tools/read.js";
-import { resizeImage } from "../src/utils/image-resize.js";
-
-const TINY_PNG_BASE64 =
-	"iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFBQIAX8jx0gAAAABJRU5ErkJggg==";
-
-describe("image resize callers", () => {
-	let testDir: string;
-
-	beforeEach(() => {
-		testDir = join(tmpdir(), `image-resize-callers-${Date.now()}`);
-		mkdirSync(testDir, { recursive: true });
-		vi.mocked(resizeImage).mockReset();
-		vi.mocked(resizeImage).mockResolvedValue(null);
-	});
-
-	afterEach(() => {
-		rmSync(testDir, { recursive: true, force: true });
-	});
-
-	it("read tool returns text-only output when auto-resize cannot produce a safe image", async () => {
-		const imagePath = join(testDir, "test.png");
-		writeFileSync(imagePath, Buffer.from(TINY_PNG_BASE64, "base64"));
-
-		const tool = createReadTool(testDir);
-		const result = await tool.execute("test-read-image", { path: imagePath });
-
-		expect(result.content).toHaveLength(1);
-		expect(result.content[0].type).toBe("text");
-		expect((result.content[0] as { type: "text"; text: string }).text).toContain("Image omitted");
-	});
-
-	it("file processor omits image attachments when auto-resize cannot produce a safe image", async () => {
-		const imagePath = join(testDir, "test.png");
-		writeFileSync(imagePath, Buffer.from(TINY_PNG_BASE64, "base64"));
-
-		const result = await processFileArguments([imagePath]);
-
-		expect(result.images).toHaveLength(0);
-		expect(result.text).toContain("Image omitted");
-	});
-});