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/web-ui/src/components/ThinkingBlock.ts

@@ -1,43 +0,0 @@
-import { icon } from "@mariozechner/mini-lit";
-import { html, LitElement } from "lit";
-import { customElement, property, state } from "lit/decorators.js";
-import { ChevronRight } from "lucide";
-
-@customElement("thinking-block")
-export class ThinkingBlock extends LitElement {
-	@property() content!: string;
-	@property({ type: Boolean }) isStreaming = false;
-	@state() private isExpanded = false;
-
-	protected override createRenderRoot(): HTMLElement | DocumentFragment {
-		return this;
-	}
-
-	override connectedCallback(): void {
-		super.connectedCallback();
-		this.style.display = "block";
-	}
-
-	private toggleExpanded() {
-		this.isExpanded = !this.isExpanded;
-	}
-
-	override render() {
-		const shimmerClasses = this.isStreaming
-			? "animate-shimmer bg-gradient-to-r from-muted-foreground via-foreground to-muted-foreground bg-[length:200%_100%] bg-clip-text text-transparent"
-			: "";
-
-		return html`
-			<div class="thinking-block">
-				<div
-					class="thinking-header cursor-pointer select-none flex items-center gap-2 py-1 text-sm text-muted-foreground hover:text-foreground transition-colors"
-					@click=${this.toggleExpanded}
-				>
-					<span class="transition-transform inline-block ${this.isExpanded ? "rotate-90" : ""}">${icon(ChevronRight, "sm")}</span>
-					<span class="${shimmerClasses}">Thinking...</span>
-				</div>
-				${this.isExpanded ? html`<markdown-block .content=${this.content} .isThinking=${true}></markdown-block>` : ""}
-			</div>
-		`;
-	}
-}