Fix printer send + live telemetry; add hardware-in-the-loop tests

[t2vi]

Confirmed end-to-end against a real Bambu P2S.

send_print: force use_ams:false in the project_file payload. A re-sliced spoolbook .3mf carries no per-filament AMS metadata, so use_ams:true fails at HMS 07FF-8012 "Failed to get AMS mapping table" regardless of ams_mapping. With it false the printer feeds from the threaded filament and the print starts. ams_mapping/ams_mapping2 now always empty.

printer_mqtt:

• max_packet_size 128KB -> 1MB. A P2S pushall full-status object overflowed 128KB, erroring the eventloop right after ConnAck -> the card flapped "Connected"/"Live" then back to "Not connected / No live job data".
• connect / ConnAck / disconnect-with-error / subscribe-fail now log; the reconnect loop was previously silent.
• publish_command uses a numeric sequence_id (submission_id()) + empty param, so the P2S actually acts on pause/resume/stop.
• connect_and_subscribe_loop + publish_raw made pub for the new tests.

printer_telemetry: record_reading no longer .expect()s its queries. It runs on the MQTT eventloop task; a DB error there unwound the whole telemetry+control connection for the printer (pause/resume/stop dead until restart). Split into try_record_reading + a wrapper that logs and drops the one reading.

PrinterCard.svelte: drop the inline live feed from the status panel. An streaming the camera is a permanent client and Bambu firmware serves one at a time, so the card starved the printer's own toolhead-camera init mid-print. Camera is popup-only now.

reslicing: slice_via_service made pub.

tests/printer_live.rs (all #[ignore], local dev only, never CI):

• live_connection_comes_up_and_stays_up
• ftps_upload_roundtrips
• send_a_print_then_cancel_before_it_extrudes
• reslice_then_print_then_cancel (unsliced .3mf -> slicer-service -> print) Print tests are triple opt-in (SPOOLBOOK_TEST_ALLOW_REAL_PRINT=1) and cancel in PREPARE before any extrusion.

examples/stop_print.rs: standalone MQTT stop command, used as the manual kill switch while developing the print path.

Closes #141 #142