docs: Comprehensive architecture documentation update

- Added detailed static scanner flow diagrams (3 Mermaid diagrams)
- Documented all configuration flags with tables and interaction matrix
- Added file selection logic diagram showing flag interactions
- Added complete data flow sequence diagram (ERB → HTML → Checks → Errors)
- Documented component interactions and integration points
- Streamlined getting started guide (478 → 346 lines, 27% reduction)
- Updated version references to 1.5.5

Architecture doc now includes:
- Complete static scanner pipeline documentation
- All flag defaults and behaviors
- Component method signatures and purposes
- Integration points with existing systems
- Performance optimization details

Author: rayraycodes