Write Migration Guide for v1.x Users

Priority: P1 - Should complete
Phase: 4 (Documentation & Release)
Parent Issue: #2044
Depends on: #2059 (breaking changes doc)

Problem

Users migrating from v1.x need a comprehensive guide to update their code and workflows.

Location

docs/interface/migration-v2.md (new file)

Sections

1. Overview

   • What changed and why
   • Benefits of v2.0.0

2. CLI Command Changes

   # v1.x
   spectrafit data.csv -i config.json
   
   # v2.0.0
   spectrafit fit data.csv -i config.json

3. Configuration File Format

   • No changes to JSON/YAML/TOML format
   • Validation is stricter

4. Python API Changes

   # v1.x
   from spectrafit.tools import run_fitting
   result = run_fitting(config_dict)
   
   # v2.0.0
   from spectrafit.core.pipeline import FittingPipeline
   from spectrafit.api.cmd_model import FittingConfig
   config = FittingConfig(**config_dict)
   result = FittingPipeline(config).run()

5. Removed Features

   • RIXS plugin
   • PPTX export
   • Alternative approaches

6. Testing Migration (for contributors)

Tasks

• Create docs/interface/migration-v2.md
• Write CLI migration section
• Write Python API migration section
• Document removed features with alternatives
• Add troubleshooting section
• Create link from main docs

Acceptance Criteria

• Complete migration guide
• All code examples tested
• Linked from main documentation
• Reviewed by maintainer