fix: replace template README for cloudflare-one-casb with real content

The `apps/cloudflare-one-casb/README.md` is still the starter template. It refers to "template-start-here" and `logpush.tools.ts`, lists no CASB tools, no remote URL, and no description of what the server does.

The server actually has 11 tools for managing CASB integrations and assets (defined in `src/tools/integrations.tools.ts`) and is live at `https://casb.mcp.cloudflare.com/mcp`. The README should reflect this.