feat: add Omega Mac native macOS SwiftUI chat app

Native macOS counterpart to the web Omega agent, connecting directly
to the OpenAI API and TPMJS tool registry (1M+ AI-ready tools).

- SwiftUI app targeting macOS 15+ with dark theme
- Full agentic loop: auto-discover tools via BM25, stream OpenAI
  responses, execute tools via remote sandbox, loop up to 10x
- SwiftData persistence for conversations, messages, tool runs
- Keychain storage for API keys and environment variables
- SSE streaming via URLSession.bytes with custom parser
- Actor-based services (OpenAIService, TPMJSRegistryService)
- NavigationSplitView layout with sidebar + chat detail
- MarkdownUI for rendering assistant responses
- Settings: API key, model picker, env vars, custom system prompt
- Keyboard shortcuts: Cmd+N new chat, Cmd+, settings, Enter send

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/omega-mac/OmegaMac/OmegaMac.entitlements

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>com.apple.security.app-sandbox</key>
+	<true/>
+	<key>com.apple.security.network.client</key>
+	<true/>
+	<key>keychain-access-groups</key>
+	<array>
+		<string>$(AppIdentifierPrefix)com.tpmjs.omega-mac</string>
+	</array>
+</dict>
+</plist>