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/validation.test.ts

@@ -1,39 +0,0 @@
-import { Type } from "@sinclair/typebox";
-import { afterEach, describe, expect, it, vi } from "vitest";
-import type { ToolCall } from "../src/types.js";
-import { validateToolArguments } from "../src/utils/validation.js";
-
-afterEach(() => {
-	vi.restoreAllMocks();
-});
-
-describe("validateToolArguments", () => {
-	it("falls back to raw arguments without writing to stderr when runtime code generation is blocked", () => {
-		const originalFunction = globalThis.Function;
-		const errorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
-		const tool = {
-			name: "echo",
-			description: "Echo tool",
-			parameters: Type.Object({
-				count: Type.Number(),
-			}),
-		};
-		const toolCall: ToolCall = {
-			type: "toolCall",
-			id: "tool-1",
-			name: "echo",
-			arguments: { count: "42" as unknown as number },
-		};
-
-		globalThis.Function = (() => {
-			throw new EvalError("Code generation from strings disallowed for this context");
-		}) as unknown as FunctionConstructor;
-
-		try {
-			expect(validateToolArguments(tool, toolCall)).toEqual(toolCall.arguments);
-			expect(errorSpy).not.toHaveBeenCalled();
-		} finally {
-			globalThis.Function = originalFunction;
-		}
-	});
-});