Add complete Calibration Suite with automated macros

New calibration system for Neptune 4 Plus:

📁 Files added:
- calibration/CALIBRATION_GUIDE.md - Complete step-by-step guide
- calibration/README.md - Installation & overview
- calibration/calibration_macros.cfg - All calibration macros
- calibration/test_patterns.cfg - Printable test patterns

🎯 Available macros:
- CALIBRATION_MENU - Main menu with all options
- CALIBRATE_Z_OFFSET - Cartographer Z0 calibration
- CALIBRATE_INPUT_SHAPER - ADXL resonance measurement
- CALIBRATE_PRESSURE_ADVANCE - PA tuning (per filament)
- CALIBRATE_FLOW_RATE - Flow rate calibration
- CALIBRATE_TEMPERATURE - Temperature tower
- CALIBRATE_RETRACTION - Retraction testing
- CALIBRATE_BED_MESH - Bed mesh verification
- CALIBRATION_FULL - Complete suite (~2.5 hours)
- CALIBRATION_QUICK - Essential calibrations (~30 min)

🔧 Test patterns:
- PA_TEST_PATTERN - Pressure Advance test squares
- FLOW_TEST_CUBE - Flow rate calibration cube
- RETRACT_TEST_PATTERN - Retraction test towers
- TEMP_TOWER - Temperature tower

✨ Features:
- Fully automated calibration sequences
- Cartographer integration for precise Z0
- Per-filament calibration support
- Clear console messages for each step
- Automatic SAVE_CONFIG reminders
- Supports both Original and Bambu hotends

Usage: Run CALIBRATION_MENU in Klipper console

calibration/README.md

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+# 🎯 Calibration Suite for Neptune 4 Plus with Cartographer
+
+## Installation
+
+1. Copy all `.cfg` files to your Klipper config directory
+2. Add `[include calibration/*.cfg]` to your `printer.cfg`
+3. Restart Klipper
+4. Run `CALIBRATION_MENU` to start
+
+---
+
+## Macros Overview
+
+- `CALIBRATION_MENU` - Main menu with all options
+- `CALIBRATE_Z_OFFSET` - Cartographer Z0 calibration
+- `CALIBRATE_INPUT_SHAPER` - ADXL resonance measurement
+- `CALIBRATE_PRESSURE_ADVANCE` - PA tuning
+- `CALIBRATE_FLOW_RATE` - Flow rate calibration
+- `CALIBRATE_TEMPERATURE` - Temperature tower
+- `CALIBRATE_RETRACTION` - Retraction tuning
+- `CALIBRATE_BED_MESH` - Bed mesh verification
+- `CALIBRATION_FULL` - Run all calibrations in sequence
+
+---
+
+## Quick Start
+
+```gcode
+; In Mainsail Console or Fluidd Console:
+CALIBRATION_MENU
+```
+
+---
+
+## Notes
+
+- All macros use Cartographer for precise measurements
+- Results are automatically saved with `SAVE_CONFIG`
+- Each macro includes safety checks and clear instructions
+- Designed for both Original and Bambu Lab hotends