Add structured logging, metrics, comprehensive testing, and Loki stack

Major improvements to observability, testing, and operational reliability:

## 🔍 Structured Logging with Tracing
- Replace all eprintln! calls with structured tracing macros across all services
- Add environment-based log level control via RUST_LOG
- Implement tracing-subscriber with env-filter, fmt, and json support
- Add tracing-log bridge for backward compatibility with existing log:: usage
- Services updated: common, weatherust, healthmon, speedynotify, updatemon, updatectl

Benefits:
- Structured logging with key-value pairs for better filtering
- Dynamic log level control without recompilation
- Consistent logging format across all services
- Better debugging with contextual information

## 📊 Prometheus Metrics Infrastructure
- Create comprehensive metrics module in common crate
- Add metrics crate dependency across all services
- Implement 12 different metric types:
  * Notification delivery tracking (success/failure rates)
  * Operation execution timing (weather API, speedtests, updates)
  * Server operation tracking (multi-server operations)
  * Container health metrics (CPU, memory, health status)
  * Update availability gauges (OS and Docker updates)
  * Speedtest result metrics (download, upload, ping, degradation)
  * Weather API performance (call count, response time)
  * Cleanup operation metrics (items removed, bytes reclaimed)
  * Webhook request metrics (endpoint, status, duration)

Benefits:
- Full operational visibility
- Performance monitoring
- Alerting capabilities (when integrated with Prometheus)
- Historical trend analysis

## 🧪 Comprehensive Testing Suite
- Add 29 new tests across 3 packages (20 → 49 total tests, +145%)
- weatherust: 13 tests for ZIP detection, city parsing, location normalization
- speedynotify: 7 tests for JSON parsing, speed degradation detection
- common: 9 tests for all metrics recording functions
- All tests passing with 100% pass rate

Benefits:
- Prevents regressions during refactoring
- Documents expected behavior
- Enables confident code changes
- Faster debugging of parsing issues

## 🔧 Loki Logging Stack (Optional)
- Add docker-compose.logging.yml for centralized log aggregation
- Configure Loki 3.0 for log storage (7-day retention)
- Configure Promtail 3.0 for automatic Docker log collection
- Configure Grafana 11.0 with Loki pre-configured as datasource
- Traefik integration for HTTPS access to Grafana
- Comprehensive LOGGING_SETUP.md guide

Benefits:
- Centralized log viewing across all containers
- Rich query capabilities with LogQL
- Time-based log exploration
- Export and analysis features

## 📝 Documentation
- Add IMPROVEMENTS_2025.md with complete implementation summary
- Add LOGGING_SETUP.md with Loki stack setup and usage guide
- Update .env.example and .env.example.short with Grafana configuration
- Migration guide for users and developers

## 🔧 Dependencies Added
Runtime:
- tracing 0.1
- tracing-subscriber 0.3 (env-filter, fmt, json)
- tracing-log 0.2
- metrics 0.23
- metrics-exporter-prometheus 0.15 (updatectl only)

Dev:
- tokio-test 0.4
- mockito 1.5 (common only)
- axum-test 15 (updatectl only)

## ✅ Quality
- All workspace crates compile successfully
- All 49 tests passing (0 failures)
- Fully backward compatible
- No breaking changes

## 🚀 Usage
Set log level: RUST_LOG=debug weatherust --zip 52726
Deploy logging: docker compose -f docker-compose.yml -f docker-compose.logging.yml up -d
View logs: https://grafana.js-node.app (or your configured domain)

🤖 Generated with Claude Code (https://claude.com/claude-code)

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

Author: jsprague84

.env.example

@@ -343,3 +343,15 @@ UPDATECTL_WEBHOOK_URL=https://webhook.js-node.app
 # HEALTHMON_TAG=
 # UPDATEMON_TAG=
 # UPDATECTL_TAG=
+
+# ============================================================================
+# Grafana & Loki Configuration (for centralized logging)
+# ============================================================================
+# Set a secure admin password for Grafana web UI
+# Default: admin (CHANGE THIS IN PRODUCTION!)
+GRAFANA_PASSWORD=admin
+
+# Domain for Grafana access via Traefik
+# Example: grafana.js-node.app
+GRAFANA_DOMAIN=grafana.localhost
+

.env.example.short

@@ -74,3 +74,8 @@ UPDATECTL_WEBHOOK_URL=https://webhook.example.com
 # HEALTHMON_TAG=
 # UPDATEMON_TAG=
 # UPDATECTL_TAG=
+
+# Grafana & Loki (optional - for centralized logging)
+GRAFANA_PASSWORD=admin
+GRAFANA_DOMAIN=grafana.localhost
+