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>

Makefile

@@ -5,7 +5,7 @@
 BINARY_NAME_AGENT = chorus-agent
 BINARY_NAME_HAP = chorus-hap
 BINARY_NAME_COMPAT = chorus
-VERSION ?= 0.5.0
+VERSION ?= 0.5.5
 COMMIT_HASH ?= $(shell git rev-parse --short HEAD 2>/dev/null || echo "unknown")
 BUILD_DATE ?= $(shell date -u '+%Y-%m-%d_%H:%M:%S')