fix: P2P connectivity regression + dynamic versioning system

## P2P Connectivity Fixes
- **Root Cause**: mDNS discovery was conditionally disabled in Task Execution Engine implementation
- **Solution**: Restored always-enabled mDNS discovery from working baseline (eb2e05f)
- **Result**: 9/9 Docker Swarm replicas with working P2P mesh, democratic elections, and leader consensus

## Dynamic Version System
- **Problem**: Hardcoded version "0.1.0-dev" in 1000+ builds made debugging impossible
- **Solution**: Implemented build-time version injection via ldflags
- **Features**: Shows commit hash, build date, and semantic version
- **Example**: `CHORUS-agent 0.5.5 (build: 9dbd361, 2025-09-26_05:55:55)`

## Container Compatibility
- **Issue**: Binary execution failed in Alpine due to glibc/musl incompatibility
- **Solution**: Added Ubuntu-based Dockerfile for proper glibc support
- **Benefit**: Reliable container execution across Docker Swarm nodes

## Key Changes
- `internal/runtime/shared.go`: Always enable mDNS discovery, dynamic version vars
- `cmd/agent/main.go`: Build-time version injection and display
- `p2p/node.go`: Restored working "🐝 Bzzz Node Status" logging format
- `Makefile`: Updated version to 0.5.5, proper ldflags configuration
- `Dockerfile.ubuntu`: New glibc-compatible container base
- `docker-compose.yml`: Updated to latest image tag for Watchtower auto-updates

## Verification
✅ P2P mesh connectivity: Peers exchanging availability broadcasts
✅ Democratic elections: Candidacy announcements and leader selection
✅ BACKBEAT integration: Beat synchronization and degraded mode handling
✅ Dynamic versioning: All containers show v0.5.5 with build metadata
✅ Task Execution Engine: All Phase 4 functionality preserved and working

Fixes P2P connectivity regression while preserving complete Task Execution Engine implementation.

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

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

cmd/agent/main.go

@@ -8,12 +8,19 @@ import (
 	"chorus/internal/runtime"
 )
 
+// Build-time variables set by ldflags
+var (
+	version    = "0.5.0-dev"
+	commitHash = "unknown"
+	buildDate  = "unknown"
+)
+
 func main() {
 	// Early CLI handling: print help/version without requiring env/config
 	for _, a := range os.Args[1:] {
 		switch a {
 		case "--help", "-h", "help":
-			fmt.Printf("%s-agent %s\n\n", runtime.AppName, runtime.AppVersion)
+			fmt.Printf("%s-agent %s (build: %s, %s)\n\n", runtime.AppName, version, commitHash, buildDate)
 			fmt.Println("Usage:")
 			fmt.Printf("  %s [--help] [--version]\n\n", filepath.Base(os.Args[0]))
 			fmt.Println("CHORUS Autonomous Agent - P2P Task Coordination")
@@ -46,11 +53,16 @@ func main() {
 			fmt.Println("  - Health monitoring")
 			return
 		case "--version", "-v":
-			fmt.Printf("%s-agent %s\n", runtime.AppName, runtime.AppVersion)
+			fmt.Printf("%s-agent %s (build: %s, %s)\n", runtime.AppName, version, commitHash, buildDate)
 			return
 		}
 	}
 
+	// Set dynamic build information
+	runtime.AppVersion = version
+	runtime.AppCommitHash = commitHash
+	runtime.AppBuildDate = buildDate
+
 	// Initialize shared P2P runtime
 	sharedRuntime, err := runtime.Initialize("agent")
 	if err != nil {