Drive Klipper, OctoPrint and PrusaLink for real

The three were println stubs. Each is now an HTTP client (Moonraker,
OctoPrint's REST API, PrusaLink's v1 API) behind a small shared helper:
status polled in the background, pause/resume/cancel, G-code lines, fan
speed, and upload-and-start of a sliced file. A slicer project (.3mf) is
refused for these, and so is an upload while a print is running.

Telemetry and the completion watcher now read a vendor-neutral
PrinterStatus instead of Bambu's PrintReport, so these printers report
progress, temperatures and job state to the cloud.

Written from the public API docs and tested against mock servers only; no
real Klipper, OctoPrint or PrusaLink machine has been on the bench.

src/completion.rs

@@ -105,7 +105,7 @@ pub async fn run(fleet: SharedFleet) {
                 if let Err(err) = printer.refresh_status().await {
                     warn!(printer = %printer.base().id, %err, "could not request a status refresh");
                 }
-                if let Some(state) = printer.print_status().await.and_then(|r| r.gcode_state) {
+                if let Some(state) = printer.status().await.and_then(|s| s.state) {
                     states.push((printer.base().id.clone(), state));
                 }
             }