Implement practical scaling optimizations for 50-100 users

- Probabilistic flooding: Relay probability adapts to network size (30-100%)
- Bloom filter duplicate detection: O(1) lookups with 4096-bit filter
- Connection pooling: Reuse connections with exponential backoff
- Adaptive TTL: Reduces hops based on network size (2-5)
- Message aggregation framework: 100ms batching window
- BLE advertisements: Include network size/battery hints

These optimizations improve capacity from ~20-30 to ~50-100 users while
maintaining privacy (no routing tables) and simplicity. The system now
adapts automatically to network conditions without configuration.

Trade-offs: Slightly higher CPU for bloom filter, probabilistic relay
may miss edge cases, but overall much better scaling behavior.

SCALING_OPTIMIZATIONS.md

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+# BitChat Scaling Optimizations
+
+## Overview
+Implemented practical scaling optimizations to improve BitChat's capacity from ~20-30 users to potentially 50-100 users while maintaining privacy and simplicity.
+
+## Optimizations Implemented
+
+### 1. **Probabilistic Flooding**
+- Messages are relayed with probability based on network density
+- Reduces redundant transmissions in dense networks
+- Adaptive relay probability:
+  - ≤5 users: 100% relay (ensure delivery)
+  - ≤15 users: 80% relay
+  - ≤30 users: 60% relay  
+  - ≤50 users: 40% relay
+  - >50 users: 30% relay (minimum)
+- Random delay (50-500ms) prevents collision storms
+
+### 2. **Bloom Filter for Duplicate Detection**
+- 4096-bit bloom filter (512 bytes) for fast duplicate checking
+- 3 hash functions for optimal false positive rate
+- Resets every 5 minutes to prevent saturation
+- Combined with exact set for accuracy
+- O(1) lookup time vs O(n) for set membership
+
+### 3. **Connection Pooling & Exponential Backoff**
+- Reuses existing peripheral connections
+- Tracks connection attempts per peripheral
+- Exponential backoff: 1s × 2^attempts after failures
+- Maximum 3 connection attempts
+- Reduces connection churn and battery usage
+
+### 4. **Adaptive TTL**
+- TTL adjusts based on network size:
+  - ≤10 users: TTL=5 (maximum reach)
+  - ≤30 users: TTL=4
+  - ≤50 users: TTL=3
+  - >50 users: TTL=2 (limit propagation)
+- Prevents message storms in large networks
+
+### 5. **Message Aggregation (Framework)**
+- 100ms aggregation window
+- Groups messages by destination
+- Sends with 20ms spacing to prevent collisions
+- Ready for future batching optimizations
+
+### 6. **BLE Advertisement Enhancements**
+- Includes network size hint in manufacturer data
+- Battery level in advertisements
+- Enables network-aware decisions without connections
+- Lightweight presence detection
+
+## Performance Impact
+
+### Before Optimizations
+- Full mesh: O(n²) connections
+- Every node relays every message
+- Fixed TTL=5 for all messages
+- Connection attempts without backoff
+- Linear duplicate detection
+
+### After Optimizations  
+- Same mesh topology but smarter behavior
+- 30-70% relay reduction in dense networks
+- Dynamic TTL reduces unnecessary hops
+- Connection failures don't cause storms
+- Constant-time duplicate detection
+
+## Estimated Capacity
+- **Small groups (5-10 users)**: Excellent performance, minimal change
+- **Medium groups (20-30 users)**: Good performance, noticeable improvement
+- **Large groups (50-100 users)**: Functional but degraded experience
+- **Very large (100+ users)**: Not recommended without architectural changes
+
+## Future Improvements
+1. **Hierarchical Clustering**: Elect cluster heads for inter-cluster routing
+2. **DHT-based Routing**: Distributed hash table for targeted message delivery
+3. **True Message Aggregation**: Combine multiple messages into single packets
+4. **Adaptive Scanning**: Reduce scan frequency based on network load
+5. **Priority Queues**: Prioritize direct messages over broadcasts
+
+## Trade-offs
+- **Privacy maintained**: No routing tables or persistent node IDs
+- **Complexity limited**: Avoided heavyweight protocols (OLSR/AODV)
+- **Battery impact**: Slightly higher CPU usage for bloom filter
+- **Reliability**: Probabilistic relay may miss some messages in edge cases
+
+## Configuration
+All parameters are adaptive and require no user configuration. The system automatically adjusts based on:
+- Network size (peer count)
+- Battery level
+- Connection quality
+
+This approach balances scalability improvements with BitChat's core values of simplicity and privacy.