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/pods/package.json

@@ -1,40 +0,0 @@
-{
-	"name": "@mariozechner/pi",
-	"version": "0.67.5",
-	"description": "CLI tool for managing vLLM deployments on GPU pods",
-	"type": "module",
-	"bin": {
-		"pi-pods": "dist/cli.js"
-	},
-	"scripts": {
-		"clean": "shx rm -rf dist",
-		"build": "tsgo -p tsconfig.build.json && shx chmod +x dist/cli.js && shx cp src/models.json dist/ && shx cp -r scripts dist/",
-		"prepublishOnly": "npm run clean && npm run build"
-	},
-	"files": [
-		"dist",
-		"scripts"
-	],
-	"keywords": [
-		"llm",
-		"vllm",
-		"gpu",
-		"ai",
-		"cli"
-	],
-	"author": "Mario Zechner",
-	"license": "MIT",
-	"repository": {
-		"type": "git",
-		"url": "git+https://github.com/badlogic/pi-mono.git",
-		"directory": "packages/pods"
-	},
-	"engines": {
-		"node": ">=20.0.0"
-	},
-	"dependencies": {
-		"@mariozechner/pi-agent-core": "^0.67.5",
-		"chalk": "^5.5.0"
-	},
-	"devDependencies": {}
-}