Web client: `aro room` server subcommand (hub)

[KrisSimon]

Context

Child of #687. Server-side counterpart of the room. Reuses the existing SwiftNIO HTTP server, the parser, the LSP wrapper, and the JSONL runtime recorder — all that already exists in this repo.

Surface

```
aro room ./MyApp # bind 127.0.0.1:PORT, print share URL
aro room ./MyApp --listen 0.0.0.0:8090 # explicit
aro room ./MyApp --token READONLY # read-only invite
```

Prints:

```
SOLARO room ready:
http://localhost:8090/?token=ab12cd34
ws://localhost:8090/rooms/main?token=ab12cd34
```

What the hub does

1. Discover the project — reuse `ApplicationLoader` (`Sources/ARORuntime/Application/ApplicationLoader.swift`).
2. Serve the web bundle — static files under `/` from the `webclient/dist` directory in the binary's resources (see Web client: aro room server subcommand (hub) #689 / Web client: "Share room" command in SOLARO #692). Falls back to a "build the web client first" page when the bundle isn't shipped.
3. Accept WebSocket upgrades on `/rooms/{id}` per the protocol in Web client: room wire protocol (WebSocket, JSON-RPC framing) #688.
4. Watch the directory — reuse `FileMonitor` (`Sources/ARORuntime/FileSystem/FileMonitor.swift`) to detect external edits and broadcast `file-changed`.
5. Tail the JSONL recorder — the runtime already writes one event per line during a recorded run (`Sources/ARORuntime/Recorder/...`). Stream those frames out as `runtime-event` messages.
6. Spawn and proxy `aro lsp` — one instance per room (not per client). `lsp` frames bounce through.
7. Persist last-seen rev per client in `~/.local/share/aro/rooms/{room-id}/state.json` so a reconnect after a disconnect skips the resend.

Things to NOT do in v1

• No multi-room. One `aro room` invocation = one project = one logical room. Multi-room is a separate process per project.
• No HTTPS / WSS termination — assume reverse proxy in production. Localhost-only by default for safety.
• No write throttling. The protocol is naive; a misbehaving client can flood — fine for the trusted-network MVP.

Files

• `Sources/AROCLI/Commands/RoomCommand.swift` (new)
• `Sources/ARORuntime/Room/RoomHub.swift` (new — owns the WebSocket fan-out, presence list, file cache)
• `Sources/ARORuntime/Room/RoomLSPBridge.swift` (new)
• `Sources/ARORuntime/Room/RoomRuntimeTap.swift` (new — subscribes to the JSONL stream)

Acceptance

• `aro room ./Examples/SimpleChat` prints a working URL.
• `websocat` against `ws://…/rooms/main` and a hand-typed `hello` frame returns `welcome` with the file list and an empty `peers` array.
• `echo "new line" >> Examples/SimpleChat/main.aro` results in a `file-changed` broadcast within 500 ms.
• Running the project through `aro run` while a client is connected delivers `runtime-event` frames matching the JSONL recorder output.