feat(distributed): add distributed mode with multi-instance coordination

Implements Phase 1 and Phase 2 of distributed enhancements for horizontal scaling:

Phase 1 - Zero-Config Distributed Mode:
- Add DistributedConfigManager for shared S3 configuration coordination
- Implement explicit role configuration (reader/writer/hybrid) for safety
- Add instance registration with heartbeat and health monitoring
- Create hash-based partitioner for deterministic data distribution

Phase 2 - Intelligent Data Management:
- Add DomainDetector for automatic data categorization (medical, legal, product, etc.)
- Implement domain-aware search filtering for improved relevance
- Create role-based operational modes with specific optimizations
- Add HealthMonitor for comprehensive metrics tracking

Key Features:
- Multi-writer support with consistent hash partitioning
- Reader instances optimize for 80% cache utilization
- Writer instances optimize for batched writes
- Automatic domain detection and tagging
- Real-time health monitoring across all instances
- Cross-platform crypto utilities for browser compatibility

Safety Improvements:
- Require explicit role configuration (no automatic assignment)
- Validate role compatibility on startup
- Track instance health and performance metrics

Testing:
- Add comprehensive test suite for distributed features
- All 25 distributed tests passing
- Fixed domain filtering in search functionality

Documentation:
- Update README with distributed mode highlights
- Add examples showing reader/writer setup
- Document new capabilities and benefits

🤖 Generated with Claude Code
https://claude.ai/code

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

src/utils/crypto.ts

@@ -0,0 +1,47 @@
+/**
+ * Cross-platform crypto utilities
+ * Provides hashing functions that work in both Node.js and browser environments
+ */
+
+/**
+ * Simple string hash function that works in all environments
+ * Uses djb2 algorithm - fast and good distribution
+ * @param str - String to hash
+ * @returns Positive integer hash
+ */
+export function hashString(str: string): number {
+  let hash = 5381
+  for (let i = 0; i < str.length; i++) {
+    const char = str.charCodeAt(i)
+    hash = ((hash << 5) + hash) + char // hash * 33 + char
+  }
+  // Ensure positive number
+  return Math.abs(hash)
+}
+
+/**
+ * Alternative: FNV-1a hash algorithm
+ * Good distribution and fast
+ * @param str - String to hash
+ * @returns Positive integer hash
+ */
+export function fnv1aHash(str: string): number {
+  let hash = 2166136261
+  for (let i = 0; i < str.length; i++) {
+    hash ^= str.charCodeAt(i)
+    hash = (hash * 16777619) >>> 0
+  }
+  return hash
+}
+
+/**
+ * Generate a deterministic hash for partitioning
+ * Uses the most appropriate algorithm for the environment
+ * @param input - Input string to hash
+ * @returns Positive integer hash suitable for modulo operations
+ */
+export function getPartitionHash(input: string): number {
+  // Use djb2 by default as it's fast and has good distribution
+  // This ensures consistent partitioning across all environments
+  return hashString(input)
+}