chore: extract arcade into standalone repo

Arcade lives as its own pnpm workspace at ~/Documents/Code/arcade
now, with no @mana/* coupling. This drops every reference and the
games/ directory from the monorepo.

Removes:
- games/ directory (89 files: web + server + 22 HTML games + screenshots)
- @arcade/web, @arcade/server pnpm workspace entries (games/* globs)
- arcade scripts in root package.json (4 scripts)
- arcade.mana.how from mana-auth trusted origins + CORS_ORIGINS
- arcade entries in mana-apps registry, app-icons, URL overrides
- arcade.mana.how from cloudflared tunnel + prometheus blackbox probes
- arcade-web service block in docker-compose.macmini.yml
- generate-env.mjs entries for arcade server + web
- BRANDING_ONLY 'arcade' entry in registry consistency spec
- dead arcade translation keys in GuestWelcomeModal (DE+EN)
- arcade mention in CLAUDE.md, authentication guideline, MODULE_REGISTRY

Verified:
- services/mana-auth/src/auth/sso-config.spec.ts: 8/8 pass
- pnpm install regenerates lockfile cleanly (-536 lines)
- no remaining 'arcade' refs outside historical snapshot docs

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/generate-env.mjs

@@ -392,36 +392,6 @@ const APP_CONFIGS = [
 		},
 	},
 
-	// Arcade Server (Hono/Bun)
-	{
-		path: 'games/arcade/apps/server/.env',
-		vars: {
-			NODE_ENV: () => 'development',
-			PORT: (env) => env.MANA_GAMES_BACKEND_PORT || '3011',
-			// Google Gemini
-			GOOGLE_GENAI_API_KEY: (env) => env.MANA_GAMES_GOOGLE_GENAI_API_KEY,
-			// Anthropic Claude
-			ANTHROPIC_API_KEY: (env) => env.MANA_GAMES_ANTHROPIC_API_KEY,
-			// Azure OpenAI
-			AZURE_OPENAI_ENDPOINT: (env) => env.MANA_GAMES_AZURE_OPENAI_ENDPOINT,
-			AZURE_OPENAI_API_KEY: (env) => env.MANA_GAMES_AZURE_OPENAI_API_KEY,
-			AZURE_OPENAI_DEPLOYMENT: (env) => env.MANA_GAMES_AZURE_OPENAI_DEPLOYMENT || 'gpt-4o',
-			// GitHub
-			GITHUB_TOKEN: (env) => env.MANA_GAMES_GITHUB_TOKEN,
-			GITHUB_OWNER: (env) => env.MANA_GAMES_GITHUB_OWNER || 'tillschneider',
-			GITHUB_REPO: (env) => env.MANA_GAMES_GITHUB_REPO || 'mana-games',
-			CORS_ORIGINS: (env) => env.CORS_ORIGINS,
-		},
-	},
-
-	// Arcade Web (Astro)
-	{
-		path: 'games/arcade/apps/web/.env',
-		vars: {
-			PUBLIC_BACKEND_URL: (env) => `http://localhost:${env.MANA_GAMES_BACKEND_PORT || '3011'}`,
-		},
-	},
-
 	// Context Server (Hono/Bun)
 	{
 		path: 'apps/context/apps/server/.env',