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/system-prompt.test.ts

@@ -1,95 +0,0 @@
-import { describe, expect, test } from "vitest";
-import { buildSystemPrompt } from "../src/core/system-prompt.js";
-
-describe("buildSystemPrompt", () => {
-	describe("empty tools", () => {
-		test("shows (none) for empty tools list", () => {
-			const prompt = buildSystemPrompt({
-				selectedTools: [],
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt).toContain("Available tools:\n(none)");
-		});
-
-		test("shows file paths guideline even with no tools", () => {
-			const prompt = buildSystemPrompt({
-				selectedTools: [],
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt).toContain("Show file paths clearly");
-		});
-	});
-
-	describe("default tools", () => {
-		test("includes all default tools when snippets are provided", () => {
-			const prompt = buildSystemPrompt({
-				toolSnippets: {
-					read: "Read file contents",
-					bash: "Execute bash commands",
-					edit: "Make surgical edits",
-					write: "Create or overwrite files",
-				},
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt).toContain("- read:");
-			expect(prompt).toContain("- bash:");
-			expect(prompt).toContain("- edit:");
-			expect(prompt).toContain("- write:");
-		});
-	});
-
-	describe("custom tool snippets", () => {
-		test("includes custom tools in available tools section when promptSnippet is provided", () => {
-			const prompt = buildSystemPrompt({
-				selectedTools: ["read", "dynamic_tool"],
-				toolSnippets: {
-					dynamic_tool: "Run dynamic test behavior",
-				},
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt).toContain("- dynamic_tool: Run dynamic test behavior");
-		});
-
-		test("omits custom tools from available tools section when promptSnippet is not provided", () => {
-			const prompt = buildSystemPrompt({
-				selectedTools: ["read", "dynamic_tool"],
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt).not.toContain("dynamic_tool");
-		});
-	});
-
-	describe("prompt guidelines", () => {
-		test("appends promptGuidelines to default guidelines", () => {
-			const prompt = buildSystemPrompt({
-				selectedTools: ["read", "dynamic_tool"],
-				promptGuidelines: ["Use dynamic_tool for project summaries."],
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt).toContain("- Use dynamic_tool for project summaries.");
-		});
-
-		test("deduplicates and trims promptGuidelines", () => {
-			const prompt = buildSystemPrompt({
-				selectedTools: ["read", "dynamic_tool"],
-				promptGuidelines: ["Use dynamic_tool for summaries.", "  Use dynamic_tool for summaries.  ", "   "],
-				contextFiles: [],
-				skills: [],
-			});
-
-			expect(prompt.match(/- Use dynamic_tool for summaries\./g)).toHaveLength(1);
-		});
-	});
-});