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/agent-session-model-switch-thinking.test.ts

@@ -1,79 +0,0 @@
-import { Agent, type ThinkingLevel } from "@mariozechner/pi-agent-core";
-import { getModel } from "@mariozechner/pi-ai";
-import { describe, expect, it } from "vitest";
-import { AgentSession } from "../src/core/agent-session.js";
-import { AuthStorage } from "../src/core/auth-storage.js";
-import { ModelRegistry } from "../src/core/model-registry.js";
-import { SessionManager } from "../src/core/session-manager.js";
-import { SettingsManager } from "../src/core/settings-manager.js";
-import { createTestResourceLoader } from "./utilities.js";
-
-const reasoningModel = getModel("anthropic", "claude-sonnet-4-5")!;
-const nonReasoningModel = getModel("anthropic", "claude-3-5-haiku-latest")!;
-
-function createSession({
-	thinkingLevel = "high",
-	defaultThinkingLevel = thinkingLevel,
-	scopedModels,
-}: {
-	thinkingLevel?: ThinkingLevel;
-	defaultThinkingLevel?: ThinkingLevel;
-	scopedModels?: Array<{ model: typeof reasoningModel; thinkingLevel?: ThinkingLevel }>;
-} = {}) {
-	const settingsManager = SettingsManager.inMemory({ defaultThinkingLevel });
-	const sessionManager = SessionManager.inMemory();
-	const authStorage = AuthStorage.inMemory();
-	authStorage.setRuntimeApiKey("anthropic", "test-key");
-	const session = new AgentSession({
-		agent: new Agent({
-			getApiKey: () => "test-key",
-			initialState: {
-				model: reasoningModel,
-				systemPrompt: "You are a helpful assistant.",
-				tools: [],
-				thinkingLevel,
-			},
-		}),
-		sessionManager,
-		settingsManager,
-		cwd: process.cwd(),
-		modelRegistry: ModelRegistry.inMemory(authStorage),
-		resourceLoader: createTestResourceLoader(),
-		scopedModels,
-	});
-
-	return { session, sessionManager, settingsManager };
-}
-
-describe("AgentSession model switching", () => {
-	it("preserves the saved thinking preference through non-reasoning models", async () => {
-		const { session, sessionManager, settingsManager } = createSession({
-			scopedModels: [{ model: reasoningModel }, { model: nonReasoningModel }],
-		});
-
-		try {
-			await session.setModel(nonReasoningModel);
-			expect(session.thinkingLevel).toBe("off");
-			expect(settingsManager.getDefaultThinkingLevel()).toBe("high");
-
-			await session.setModel(reasoningModel);
-			expect(session.thinkingLevel).toBe("high");
-
-			await session.cycleModel();
-			expect(session.thinkingLevel).toBe("off");
-			expect(settingsManager.getDefaultThinkingLevel()).toBe("high");
-
-			await session.cycleModel();
-			expect(session.thinkingLevel).toBe("high");
-			expect(settingsManager.getDefaultThinkingLevel()).toBe("high");
-			expect(
-				sessionManager
-					.getEntries()
-					.filter((entry) => entry.type === "thinking_level_change")
-					.map((entry) => entry.thinkingLevel),
-			).toEqual(["off", "high", "off", "high"]);
-		} finally {
-			session.dispose();
-		}
-	});
-});