docs: Consolidate roadmaps and refactor documentation structure

MAJOR REFACTORING: Merge 3 roadmap files into single comprehensive ROADMAP.md

Changes:
- Merged ROADMAP.md + FLEXIBLE_ROADMAP.md + FUTURE_RELEASES.md → ROADMAP.md
- Consolidated 1,008 lines across 3 files into 429 lines (single source of truth)
- Removed duplicate/overlapping content
- Cleaned up docs archive structure

New ROADMAP.md Structure:
- Current Status (v2.6.0)
- Development Philosophy (task-based approach)
- Task-Based Roadmap (136 tasks, 10 categories)
- Release History (v1.0.0, v2.1.0, v2.6.0)
- Release Planning (v2.7-v2.9)
- Long-term Vision (v3.0+)
- Metrics & Goals
- Contribution guidelines

Deleted Files:
- FLEXIBLE_ROADMAP.md (merged into ROADMAP.md)
- FUTURE_RELEASES.md (merged into ROADMAP.md)
- docs/archive/temp/TERMINAL_SELECTION.md (temporary file)
- docs/archive/temp/TESTING.md (temporary file)

Moved Files:
- docs/plans/*.md → docs/archive/plans/ (dated planning docs)

Updated References:
- CLAUDE.md: FLEXIBLE_ROADMAP.md → ROADMAP.md
- docs/README.md: Removed duplicate roadmap references
- CHANGELOG.md: Updated documentation references

Benefits:
- Single source of truth for roadmap
- No duplicate maintenance
- Cleaner repository structure
- Better discoverability
- Historical context preserved in archive/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/README.md

@@ -80,9 +80,7 @@ Historical documentation and completed features:
 
 Want to contribute? See:
 - [Contributing Guide](../CONTRIBUTING.md) - Contribution guidelines
-- [Roadmap](../ROADMAP.md) - Project roadmap
-- [Flexible Roadmap](../FLEXIBLE_ROADMAP.md) - Detailed task list (134 tasks)
-- [Future Releases](../FUTURE_RELEASES.md) - Planned features
+- [Roadmap](../ROADMAP.md) - Comprehensive roadmap with 136 tasks
 
 ## 📝 Changelog