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/src/stream.ts

@@ -1,59 +0,0 @@
-import "./providers/register-builtins.js";
-
-import { getApiProvider } from "./api-registry.js";
-import type {
-	Api,
-	AssistantMessage,
-	AssistantMessageEventStream,
-	Context,
-	Model,
-	ProviderStreamOptions,
-	SimpleStreamOptions,
-	StreamOptions,
-} from "./types.js";
-
-export { getEnvApiKey } from "./env-api-keys.js";
-
-function resolveApiProvider(api: Api) {
-	const provider = getApiProvider(api);
-	if (!provider) {
-		throw new Error(`No API provider registered for api: ${api}`);
-	}
-	return provider;
-}
-
-export function stream<TApi extends Api>(
-	model: Model<TApi>,
-	context: Context,
-	options?: ProviderStreamOptions,
-): AssistantMessageEventStream {
-	const provider = resolveApiProvider(model.api);
-	return provider.stream(model, context, options as StreamOptions);
-}
-
-export async function complete<TApi extends Api>(
-	model: Model<TApi>,
-	context: Context,
-	options?: ProviderStreamOptions,
-): Promise<AssistantMessage> {
-	const s = stream(model, context, options);
-	return s.result();
-}
-
-export function streamSimple<TApi extends Api>(
-	model: Model<TApi>,
-	context: Context,
-	options?: SimpleStreamOptions,
-): AssistantMessageEventStream {
-	const provider = resolveApiProvider(model.api);
-	return provider.streamSimple(model, context, options);
-}
-
-export async function completeSimple<TApi extends Api>(
-	model: Model<TApi>,
-	context: Context,
-	options?: SimpleStreamOptions,
-): Promise<AssistantMessage> {
-	const s = streamSimple(model, context, options);
-	return s.result();
-}