Implement deprecation strategy and migration support

[goruha]

Description

Create comprehensive migration support for users upgrading from old API.

Tasks

• Add deprecation warnings to all old APIs
• Document deprecation timeline in CHANGELOG.md
• Create foapy/utils/migration.py with helper functions
• Build CLI tool: foapy-migrate for auto-updating code
• Provide codemods for common patterns
• Create detailed migration guide with examples
• Test migration on sample projects
• Document breaking changes clearly
• Plan for removal in version 0.3.0

Dependencies

• Requires: All new modules implemented
• Requires: Documentation complete

Related to

Phase 6: Migration and Deprecation

Acceptance Criteria

• Deprecation warnings are clear and actionable
• Migration tools successfully update sample code
• Migration guide is comprehensive
• Timeline is clearly communicated
• No surprises for users