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/package.json

@@ -1,51 +0,0 @@
-{
-	"name": "@mariozechner/pi-web-ui",
-	"version": "0.67.5",
-	"description": "Reusable web UI components for AI chat interfaces powered by @mariozechner/pi-ai",
-	"type": "module",
-	"main": "dist/index.js",
-	"types": "dist/index.d.ts",
-	"exports": {
-		".": "./dist/index.js",
-		"./app.css": "./dist/app.css"
-	},
-	"scripts": {
-		"clean": "shx rm -rf dist",
-		"build": "tsc -p tsconfig.build.json && tailwindcss -i ./src/app.css -o ./dist/app.css --minify",
-		"dev": "concurrently --names \"build,example\" --prefix-colors \"cyan,green\" \"tsc -p tsconfig.build.json --watch --preserveWatchOutput\" \"tailwindcss -i ./src/app.css -o ./dist/app.css --watch\" \"npm run dev --prefix example\"",
-		"dev:tsc": "concurrently --names \"build\" --prefix-colors \"cyan\" \"tsc -p tsconfig.build.json --watch --preserveWatchOutput\" \"tailwindcss -i ./src/app.css -o ./dist/app.css --watch\"",
-		"check": "biome check --write --error-on-warnings . && tsc --noEmit && cd example && biome check --write --error-on-warnings . && tsc --noEmit"
-	},
-	"dependencies": {
-		"@lmstudio/sdk": "^1.5.0",
-		"@mariozechner/pi-ai": "^0.67.5",
-		"@mariozechner/pi-tui": "^0.67.5",
-		"docx-preview": "^0.3.7",
-		"jszip": "^3.10.1",
-		"lucide": "^0.544.0",
-		"ollama": "^0.6.0",
-		"pdfjs-dist": "5.4.394",
-		"xlsx": "https://cdn.sheetjs.com/xlsx-0.20.3/xlsx-0.20.3.tgz"
-	},
-	"peerDependencies": {
-		"@mariozechner/mini-lit": "^0.2.0",
-		"lit": "^3.3.1"
-	},
-	"devDependencies": {
-		"@mariozechner/mini-lit": "^0.2.0",
-		"@tailwindcss/cli": "^4.0.0-beta.14",
-		"concurrently": "^9.2.1",
-		"typescript": "^5.7.3"
-	},
-	"keywords": [
-		"ai",
-		"chat",
-		"ui",
-		"components",
-		"llm",
-		"web-components",
-		"mini-lit"
-	],
-	"author": "Mario Zechner",
-	"license": "MIT"
-}