feat: add v5.8.0 features - transactions, pagination, and comprehensive docs

**Transaction System (TIER 1.2)**
- Atomic operations with automatic rollback
- 36 unit tests + 35 integration tests passing
- Full documentation in docs/transactions.md

**Duplicate Check Optimization (TIER 1.4)**
- Optimized from O(n) to O(log n) using GraphAdjacencyIndex
- Uses LSM-tree for efficient lookups
- Tests verify performance improvements

**GraphIndex Pagination (TIER 1.5)**
- Production-scale pagination for high-degree nodes
- Backward compatible API
- 18 pagination tests passing

**Comprehensive Filter Documentation (TIER 1.6)**
- Complete operator reference (15 operators)
- Compound filters (anyOf, allOf, nested logic)
- Common query patterns and troubleshooting guide
- 642 lines of new documentation

**README Updates**
- Added Filter & Query Syntax Guide to Essential Reading
- Added Transactions to Core Concepts section

All changes tested and production-ready for v5.8.0 release.

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

Co-Authored-By: Claude <noreply@anthropic.com>

src/transaction/index.ts

@@ -0,0 +1,32 @@
+/**
+ * Transaction System
+ *
+ * Provides atomicity for Brainy operations.
+ * All operations succeed or all rollback - no partial failures.
+ *
+ * @module transaction
+ */
+
+export * from './types.js'
+export * from './errors.js'
+export { Transaction } from './Transaction.js'
+export { TransactionManager, type TransactionStats } from './TransactionManager.js'
+
+// Re-export for convenience
+export type {
+  Operation,
+  RollbackAction,
+  TransactionState,
+  TransactionContext,
+  TransactionFunction,
+  TransactionResult,
+  TransactionOptions
+} from './types.js'
+
+export {
+  TransactionError,
+  TransactionExecutionError,
+  TransactionRollbackError,
+  InvalidTransactionStateError,
+  TransactionTimeoutError
+} from './errors.js'