docs: Restructure documentation into focused guides (#15)

* docs: Restructure documentation into focused guides

Split the 539-line README into focused documentation:

Created new documentation structure:
- docs/presets.md (11KB) - Complete preset strategies guide
  * All 6 presets with detailed criteria
  * Use cases and best practices
  * Performance characteristics (column counts)
  * Usage examples and typical results

- docs/fields.md (16KB) - Comprehensive field reference
  * All 75+ fields organized by category
  * Field variants (TTM/FQ/FY) explained in depth
  * Usage tips and screening examples
  * Type information and typical value ranges

- docs/development.md (15KB) - Development guide
  * Local setup and MCP configuration
  * Development workflow and testing
  * Adding new fields, presets, and tools
  * Debugging and troubleshooting

Updated README (539 → 263 lines, 51% reduction):
- Quick-start focused with essential info
- Added Documentation section with links to guides
- Simplified configuration examples
- Condensed preset and field information into tables
- Added links to detailed docs throughout
- Maintained all critical information while improving discoverability

Benefits:
✓ Better organization and navigation
✓ Easier to find specific information
✓ README remains quick-start focused
✓ Comprehensive docs for deep dives
✓ Scalable structure for future additions

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

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

* docs: Fix documentation issues from code review

- Remove broken links to non-existent local documentation files
- Fix broken anchor link (usage-examples → quick-start)
- Correct field name: Net Margin → After-Tax Margin in quality_stocks preset
- Add missing after_tax_margin field documentation

Co-authored-by: Pavel Fadeev <bearmug@users.noreply.github.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Pavel Fadeev <bearmug@users.noreply.github.com>

Author: 3 people