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/interactive-mode-compaction.test.ts

@@ -1,57 +0,0 @@
-import { describe, expect, test, vi } from "vitest";
-import { InteractiveMode } from "../src/modes/interactive/interactive-mode.js";
-
-describe("InteractiveMode compaction events", () => {
-	test("rebuilds chat and appends a synthetic compaction summary at the bottom", async () => {
-		const fakeThis = {
-			isInitialized: true,
-			footer: { invalidate: vi.fn() },
-			autoCompactionEscapeHandler: undefined as (() => void) | undefined,
-			autoCompactionLoader: undefined,
-			defaultEditor: {},
-			statusContainer: { clear: vi.fn() },
-			chatContainer: { clear: vi.fn() },
-			rebuildChatFromMessages: vi.fn(),
-			addMessageToChat: vi.fn(),
-			showError: vi.fn(),
-			showStatus: vi.fn(),
-			flushCompactionQueue: vi.fn().mockResolvedValue(undefined),
-			ui: { requestRender: vi.fn() },
-		};
-
-		const handleEvent = Reflect.get(InteractiveMode.prototype, "handleEvent") as (
-			this: typeof fakeThis,
-			event: {
-				type: "compaction_end";
-				reason: "manual" | "threshold" | "overflow";
-				result: { tokensBefore: number; summary: string } | undefined;
-				aborted: boolean;
-				willRetry: boolean;
-				errorMessage?: string;
-			},
-		) => Promise<void>;
-
-		await handleEvent.call(fakeThis, {
-			type: "compaction_end",
-			reason: "manual",
-			result: {
-				tokensBefore: 123,
-				summary: "summary",
-			},
-			aborted: false,
-			willRetry: false,
-		});
-
-		expect(fakeThis.chatContainer.clear).toHaveBeenCalledTimes(1);
-		expect(fakeThis.rebuildChatFromMessages).toHaveBeenCalledTimes(1);
-		expect(fakeThis.addMessageToChat).toHaveBeenCalledTimes(1);
-		expect(fakeThis.addMessageToChat).toHaveBeenCalledWith(
-			expect.objectContaining({
-				role: "compactionSummary",
-				tokensBefore: 123,
-				summary: "summary",
-			}),
-		);
-		expect(fakeThis.flushCompactionQueue).toHaveBeenCalledWith({ willRetry: false });
-	});
-});