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/compaction-summary-reasoning.test.ts

@@ -1,78 +0,0 @@
-import type { AgentMessage } from "@mariozechner/pi-agent-core";
-import type { AssistantMessage, Model } from "@mariozechner/pi-ai";
-import { beforeEach, describe, expect, it, vi } from "vitest";
-import { generateSummary } from "../src/core/compaction/index.js";
-
-const { completeSimpleMock } = vi.hoisted(() => ({
-	completeSimpleMock: vi.fn(),
-}));
-
-vi.mock("@mariozechner/pi-ai", async (importOriginal) => {
-	const actual = await importOriginal<typeof import("@mariozechner/pi-ai")>();
-	return {
-		...actual,
-		completeSimple: completeSimpleMock,
-	};
-});
-
-function createModel(reasoning: boolean): Model<"anthropic-messages"> {
-	return {
-		id: reasoning ? "reasoning-model" : "non-reasoning-model",
-		name: reasoning ? "Reasoning Model" : "Non-reasoning Model",
-		api: "anthropic-messages",
-		provider: "anthropic",
-		baseUrl: "https://api.anthropic.com",
-		reasoning,
-		input: ["text"],
-		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
-		contextWindow: 200000,
-		maxTokens: 8192,
-	};
-}
-
-const mockSummaryResponse: AssistantMessage = {
-	role: "assistant",
-	content: [{ type: "text", text: "## Goal\nTest summary" }],
-	api: "anthropic-messages",
-	provider: "anthropic",
-	model: "claude-sonnet-4-5",
-	usage: {
-		input: 10,
-		output: 10,
-		cacheRead: 0,
-		cacheWrite: 0,
-		totalTokens: 20,
-		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
-	},
-	stopReason: "stop",
-	timestamp: Date.now(),
-};
-
-const messages: AgentMessage[] = [{ role: "user", content: "Summarize this.", timestamp: Date.now() }];
-
-describe("generateSummary reasoning options", () => {
-	beforeEach(() => {
-		completeSimpleMock.mockReset();
-		completeSimpleMock.mockResolvedValue(mockSummaryResponse);
-	});
-
-	it("sets reasoning=high for reasoning-capable models", async () => {
-		await generateSummary(messages, createModel(true), 2000, "test-key");
-
-		expect(completeSimpleMock).toHaveBeenCalledTimes(1);
-		expect(completeSimpleMock.mock.calls[0][2]).toMatchObject({
-			reasoning: "high",
-			apiKey: "test-key",
-		});
-	});
-
-	it("does not set reasoning for non-reasoning models", async () => {
-		await generateSummary(messages, createModel(false), 2000, "test-key");
-
-		expect(completeSimpleMock).toHaveBeenCalledTimes(1);
-		expect(completeSimpleMock.mock.calls[0][2]).toMatchObject({
-			apiKey: "test-key",
-		});
-		expect(completeSimpleMock.mock.calls[0][2]).not.toHaveProperty("reasoning");
-	});
-});