refactor: switched to upstream @mariozechner/pi-ai and removed unused packages

- Replaced local @oh-my-pi/pi-ai with upstream @mariozechner/pi-ai@0.37.4
- Added sessionId support to agent for provider caching (OpenAI Codex)
- Deleted packages/ai (now using upstream)
- Deleted packages/mom (unused)
- Deleted packages/web-ui (unused)

packages/coding-agent/package.json

@@ -39,8 +39,8 @@
 		"prepublishOnly": "bun run generate-template && bun run clean && bun run build"
 	},
 	"dependencies": {
+		"@mariozechner/pi-ai": "^0.37.4",
 		"@oh-my-pi/pi-agent-core": "workspace:*",
-		"@oh-my-pi/pi-ai": "workspace:*",
 		"@oh-my-pi/pi-git-tool": "workspace:*",
 		"@oh-my-pi/pi-tui": "workspace:*",
 		"@openai/agents": "^0.3.7",