docs: Add comprehensive concurrency, limitations, and competitive analysis

Added three major documentation files informed by real-world production experience:

**CONCURRENCY-BEST-PRACTICES.md** (500+ lines)
- WAL mode configuration and best practices
- Three locking strategies: No-Lock, Optimistic (retry), Pessimistic (queue)
- Based on Jellyfin's SQLite locking analysis
- Transaction batching patterns (20x speedup)
- Multi-process architecture patterns
- Production monitoring and debugging
- Decision matrix for strategy selection

**COMPETITIVE-ANALYSIS.md** (400+ lines)
- Comparison with Neo4j, ArangoDB, OrientDB, Memgraph, TinkerPop, gun.js, level-graph
- 20+ dimension comparison matrix
- Performance benchmarks across solutions
- Resource usage comparisons (500x smaller, 3000x faster startup)
- Use case decision matrices
- Market positioning as "High-Performance Embedded"

**LIMITATIONS.md** (500+ lines)
- Critical limitations with code examples
- Enhanced concurrency section with Jellyfin findings
- WAL mode, retry logic, and write queue patterns
- Scale limits and performance degradation tables
- Security, operational, and performance concerns
- Mitigation strategies and workarounds
- Severity classifications and decision matrices

**README.md Updates**
- Added links to new documentation
- Organized docs section with clear descriptions

References:
- Jellyfin SQLite locking: https://jellyfin.org/posts/SQLite-locking/
- Real-world production patterns for high-concurrency scenarios
- 7.11x index speedup findings from benchmark suite

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

Co-Authored-By: Claude <[email protected]>

Author: michaeloboyle

README.md

@@ -132,6 +132,9 @@ See [SPARC-DEVELOPMENT.md](docs/SPARC-DEVELOPMENT.md) for detailed methodology d
 - [Development Plan](PLAN.md) - Comprehensive project roadmap
 - [SPARC Methodology](docs/SPARC-DEVELOPMENT.md) - Development approach
 - [Performance Benchmarks](docs/BENCHMARKS.md) - Detailed performance analysis and methodology
+- [Concurrency Best Practices](docs/CONCURRENCY-BEST-PRACTICES.md) - Production concurrency patterns and WAL mode
+- [Limitations](docs/LIMITATIONS.md) - Known limitations and workarounds
+- [Competitive Analysis](docs/COMPETITIVE-ANALYSIS.md) - Comparison with Neo4j, ArangoDB, and alternatives
 - [API Reference](docs/API.md) - Full API documentation (1,398 lines)
 - [Examples](examples/) - Usage examples including 750-line job pipeline