Replace the infinite fixed-delay retry loop with exponential backoff
(1s, 2s, 4s, ... capped at 60s) and a max retry limit of 10.
Changes to SiloEventListener:
- Expand connection_status signal to (status, retry_count, error_message)
- Add exponential backoff: min(BASE_DELAY * 2^retries, MAX_DELAY)
- Add terminal "gave_up" state after MAX_RETRIES exhausted
- Capture and forward error messages from failed connection attempts
Changes to SiloAuthDockWidget._on_sse_status:
- Show retry count: "Reconnecting (3/10)..."
- Show "Disconnected" (red) on gave_up state
- Log each attempt to FreeCAD console (PrintWarning/PrintError)
- Set tooltip with last error message on the status label
Closes#2
