Fix calibration to include lon/lat params and document motor init flow

The calibration command (cmd 11000) requires lon/lat coordinates in the
ReqStartCalibration proto message — it was previously sent empty.
Added StartCalibrationWithLocation(lon, lat) method and updated the CLI.

Confirmed the complete motor initialization flow:
1. NEED_RESET (-14520) is NORMAL after every power-on
2. Slew (joystick) works in relative mode without absolute position
3. Only a successful astro calibration (night + stars + lon/lat) homes
   the motors and provides absolute positioning
4. After calibration, motor position returns code=0 with real coordinates
5. GoTo and tracking require calibration first
6. There is NO API command to initialize motors in daytime — the official
   app works identically (relative slew until night calibration)

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

dwarfctl/internal/api/client.go

@@ -238,9 +238,16 @@ func (t *Telescope) SetFocusInfinityPos(pos int32) error {
 
 // --- Astro commands ---
 
-// StartCalibration begins star calibration.
+// StartCalibration begins star calibration. Requires lon/lat and a starry sky.
+// This is the ONLY way to home motors and get absolute positioning.
 func (t *Telescope) StartCalibration() error {
-	_, err := t.sendEmpty(CmdAstroStartCalibration)
+	_, err := t.send(CmdAstroStartCalibration, &pb.ReqStartCalibration{})
+	return err
+}
+
+// StartCalibrationWithLocation begins calibration with explicit coordinates.
+func (t *Telescope) StartCalibrationWithLocation(lon, lat float64) error {
+	_, err := t.send(CmdAstroStartCalibration, &pb.ReqStartCalibration{Lon: lon, Lat: lat})
 	return err
 }