[DEVEX] Locally serve API and frontend via `hatchet-dashboard`

[gregfurman]

Is your feature request related to a problem? Please describe.

Running Hatchet's frontend locally requires spinning up hatchet-server and frontend/app as separate processes, plus a Caddy reverse proxy to route app.dev.hatchet-tools.com to localhost.

This is unnecessarily complex when the hatchet-dashboard binary already serves both the API and frontend together.

Describe the solution you'd like

Use the hatchet-dashboard binary to serve both the API and frontend directly over localhost, eliminating the need for Caddy, hostname aliasing, and managing separate (and tightly coupled) processes.

Describe alternatives you've considered
N/A

Additional context

See discussion #2972 (comment)