refine(skills): lang-sparql-dev - expand pillar coverage (2/8)

## Summary

`lang-sparql-dev` has 2/8 pillar coverage and needs expansion.

## Current Coverage

- ✗ Module System
- ✓ Error Handling
- ✗ Concurrency
- ✗ Metaprogramming
- ✗ Zero/Default Values
- ✗ Serialization
- ✓ Build/Dependencies
- ✗ Testing

## Refinement Checklist

- [ ] Add Module System section (namespaces, prefixes, imports)
- [ ] Add Concurrency section (SPARQL endpoints, async queries)
- [ ] Add Metaprogramming section (CONSTRUCT, templates)
- [ ] Add Zero/Default Values section (OPTIONAL, COALESCE, bound())
- [ ] Add Serialization section (result formats: JSON, XML, CSV)
- [ ] Add Testing section (query validation, test frameworks)
- [ ] Run `just validate-pillars lang-sparql-dev` to verify coverage
- [ ] Ensure SKILL.md is under 500 lines (use progressive disclosure)

## Validation Command

```bash
just validate-pillars lang-sparql-dev
```