docs: Add SPARC Phase 3 Architecture design

Complete architecture design for pattern matching and bulk operations:

Pattern Matching Architecture:
- PatternQuery fluent API (Cypher-style)
- PatternParser: Parse pattern strings to AST
- SQLGenerator: Convert patterns to optimized SQL
- PatternMatcher: Execute queries
- ResultBuilder: Map SQL rows to typed results

Bulk Operations Architecture:
- BulkOperations: High-level API for bulk CRUD
- BulkProcessor: Transaction wrapping and batching
- BulkValidator: Input validation
- Prepared statement reuse for performance

Type System:
- Pattern matching types (NodePattern, EdgePattern, PathPattern)
- Bulk operation types (BulkNodeInput, BulkNodeResult, etc.)
- Error types (PatternSyntaxError, BulkOperationError)

Implementation Sequence:
- Week 1-2: Pattern matching (parser, SQL gen, query API)
- Week 3: Bulk operations (create, update, delete)
- Week 4: Integration, testing, release

Design decisions:
- Minimal breaking changes (additive API)
- Performance first (indexes, prepared stmts)
- Type-safe generics throughout
- Self-contained modules

Ready for Refinement phase (TDD implementation).

Author: michaeloboyle