fix: Phase 2 - DRC API fix and JLCPCB documentation restructure (#33, #34, #43)

Phase 2 medium-priority fixes addressing three issues:

Issue #33 - DRC violations API broken in KiCAD 9.0:
- Reimplemented get_drc_violations() to use run_drc() internally
- run_drc uses kicad-cli which is stable across KiCAD versions
- Maintains backward compatibility while fixing GetDRCMarkers() issue
- Added documentation to KNOWN_ISSUES.md
- Returns violations in original format by parsing kicad-cli JSON output

Issue #34 - JLCPCB API documentation misleading:
- Restructured README and JLCPCB_USAGE_GUIDE.md
- Now leads with JLCSearch public API (no authentication required)
- Moved official JLCPCB API to "Advanced" section with clear requirements
- Clarified that official API requires enterprise account + order history
- Makes it easier for new users to get started

Issue #43 - JLCPCB part count documentation inaccurate:
- Updated all "100k+" references to "2.5M+" (accurate catalog size)
- Updated download time estimates to 40-60 minutes
- Updated expected database size to 1-2 GB
- Clarified 100-part pagination limit in JLCSearch API

Documentation changes:
- README.md: Updated JLCPCB integration section
- docs/JLCPCB_USAGE_GUIDE.md: Complete restructure with 3 approaches
- docs/KNOWN_ISSUES.md: Added DRC fix documentation

All changes improve user experience and documentation accuracy.

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

docs/KNOWN_ISSUES.md

@@ -101,6 +101,12 @@ Schematic operations use the kicad-skip library which has some limitations with
 
 ## Recently Fixed
 
+### DRC Violations API KiCAD 9.0 (Fixed 2026-02-26)
+
+**Was:** `get_drc_violations` failed with `AttributeError: 'BOARD' object has no attribute 'GetDRCMarkers'`
+**Now:** Reimplemented to use `run_drc()` internally which calls kicad-cli
+**Impact:** Maintains backward compatibility while using stable kicad-cli interface
+
 ### Component Library Integration (Fixed 2025-11-01)
 
 **Was:** Could not find footprint libraries