feat: Implement CHORUS scaling improvements for robust autoscaling

Address WHOOSH issue #7 with comprehensive scaling optimizations to prevent
license server, bootstrap peer, and control plane collapse during fast scale-out.

HIGH-RISK FIXES (Must-Do):
✅ License gate already implemented with cache + circuit breaker + grace window
✅ mDNS disabled in container environments (CHORUS_MDNS_ENABLED=false)
✅ Connection rate limiting (5 dials/sec, 16 concurrent DHT queries)
✅ Connection manager with watermarks (32 low, 128 high)
✅ AutoNAT enabled for container networking

MEDIUM-RISK FIXES (Next Priority):
✅ Assignment merge layer with HTTP/file config + SIGHUP reload
✅ Runtime configuration system with WHOOSH assignment API support
✅ Election stability windows to prevent churn:
  - CHORUS_ELECTION_MIN_TERM=30s (minimum time between elections)
  - CHORUS_LEADER_MIN_TERM=45s (minimum time before challenging healthy leader)
✅ Bootstrap pool JSON support with priority sorting and join stagger

NEW FEATURES:
- Runtime config system with assignment overrides from WHOOSH
- SIGHUP reload handler for live configuration updates
- JSON bootstrap configuration with peer metadata (region, roles, priority)
- Configurable election stability windows with environment variables
- Multi-format bootstrap support: Assignment → JSON → CSV

FILES MODIFIED:
- pkg/config/assignment.go (NEW): Runtime assignment merge system
- docker/bootstrap.json (NEW): Example JSON bootstrap configuration
- pkg/election/election.go: Added stability windows and churn prevention
- internal/runtime/shared.go: Integrated assignment loading and conditional mDNS
- p2p/node.go: Added connection management and rate limiting
- pkg/config/hybrid_config.go: Added rate limiting configuration fields
- docker/docker-compose.yml: Updated environment variables and configs
- README.md: Updated status table with scaling milestone

This implementation enables wave-based autoscaling without system collapse,
addressing all scaling concerns from WHOOSH issue #7.

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

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

docker/bootstrap.json

@@ -0,0 +1,38 @@
+{
+  "metadata": {
+    "generated_at": "2024-12-19T10:00:00Z",
+    "cluster_id": "production-cluster",
+    "version": "1.0.0",
+    "notes": "Bootstrap configuration for CHORUS scaling - managed by WHOOSH"
+  },
+  "peers": [
+    {
+      "address": "/ip4/10.0.1.10/tcp/9000/p2p/12D3KooWExample1234567890abcdef",
+      "priority": 100,
+      "region": "us-east-1",
+      "roles": ["admin", "stable"],
+      "enabled": true
+    },
+    {
+      "address": "/ip4/10.0.1.11/tcp/9000/p2p/12D3KooWExample1234567890abcde2",
+      "priority": 90,
+      "region": "us-east-1",
+      "roles": ["worker", "stable"],
+      "enabled": true
+    },
+    {
+      "address": "/ip4/10.0.2.10/tcp/9000/p2p/12D3KooWExample1234567890abcde3",
+      "priority": 80,
+      "region": "us-west-2",
+      "roles": ["worker", "stable"],
+      "enabled": true
+    },
+    {
+      "address": "/ip4/10.0.3.10/tcp/9000/p2p/12D3KooWExample1234567890abcde4",
+      "priority": 70,
+      "region": "eu-central-1",
+      "roles": ["worker"],
+      "enabled": false
+    }
+  ]
+}