Add a reference page for the 'start' command

[Swiftaxe]

There is a need for a page listing all the options when using the 'serverpod start' command:

command: serverpod start
usage: serverpod start [options] [-- ]

Options:

watch:
flags: ["-w", "--watch", "--no-watch"]
type: boolean
default: true
description: "Enable file watching + incremental compilation (Frontend Server)."

directory:
flags: ["-d", "--directory"]
type: string
default: ""
description: "Server directory (auto-detected when empty)."

docker:
flags: ["--docker", "--no-docker"]
type: boolean
default: false
description: "Start Docker Compose services if docker-compose.yaml exists."

tui:
flags: ["--tui", "--no-tui"]
type: boolean
default: true
description: "Enable interactive terminal UI."

flutter:
flags: ["--flutter", "--no-flutter"]
type: boolean
default: true
description: "Launch companion Flutter app when available."

flutter-device:
flags: ["--flutter-device"]
type: string
default: "chrome"
description: "Device passed to flutter run -d."

flutter-option:
flags: ["--flutter-option"]
type: array
default: []
repeatable: true
description: "Extra argument(s) forwarded to flutter run."

passthrough:
server_args:
separator: "--"
description: "Arguments after '--' are passed to the server process."