Add per-series chart pattern styles

[terzioglub]

Summary

• add seriesStyles to dashboard YAML/JSON schema, Go widget model, and TSX loader
• render dashed/dotted line styles and striped/hatched fill patterns in Recharts charts, legends, and tooltips
• document YAML/TSX usage and add focused loader/validator tests

Tests

• PATH=/tmp/go1.25.0/bin:$PATH go test ./cmd/... ./pkg/... ./schemas/...
• npm run typecheck
• npm run lint
• npm run build