feat: Universal auto-instrumentation for all languages

## New Features

### Universal Instrumentation Container
- Created deploy/instrumentation/ with Dockerfile that downloads OTel agents for:
  - .NET (glibc and musl/Alpine versions)
  - Node.js (with auto-instrumentation package)
  - Python (bootstrap script + requirements)
  - Java (javaagent JAR)
  - Go (example code for compile-time instrumentation)
  - PHP (composer package + init script)

### Universal instrument.sh Script
- Auto-detects application language from running processes
- Generates docker-compose snippets for each language
- Supports: dotnet, nodejs, python, java, go, php
- Usage: ./instrument.sh <container> [language] [otlp_endpoint]

### Improved docker-compose.yml
- Added instrumentation init container with shared volume
- Added AGENT_KEY environment variable for proper auth
- Added ophion-agent service for host metrics collection
- Named containers for easier management
- Added ophion-network for service discovery

### Documentation
- Created docs/QUICK_START.md with:
  - Single-command installation
  - Instrumentation guide for all languages
  - Troubleshooting section
  - Authentication guide

### Auth Fixes
- Server now properly validates AGENT_KEY for agent authentication
- OTel Collector configured with AGENT_KEY for forwarding to server
- Fixed 401 errors when agents connect

## Files Changed
- docker-compose.yml: Complete stack with all services
- deploy/instrumentation/*: Universal OTel agent container
- deploy/docker/otel-collector-config.yaml: Fixed auth headers
- instrument.sh: Universal instrumentation script
- docs/QUICK_START.md: Complete quick start guide
- README.md: Updated with new features
- .env.example: Added AGENT_KEY

## Testing
- Go code compiles successfully
- Docker images build correctly
- All changes are backwards compatible

deploy/instrumentation/files/go/go.mod.example

@@ -0,0 +1,5 @@
+// Add these to your go.mod:
+// go get go.opentelemetry.io/otel
+// go get go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp
+// go get go.opentelemetry.io/otel/sdk/trace
+// go get go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp

deploy/instrumentation/files/go/init.go.example

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"context"
+	"os"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
+	"go.opentelemetry.io/otel/sdk/resource"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	semconv "go.opentelemetry.io/otel/semconv/v1.17.0"
+)
+
+func InitTracing(serviceName string) (*sdktrace.TracerProvider, error) {
+	ctx := context.Background()
+
+	exporter, err := otlptracehttp.New(ctx,
+		otlptracehttp.WithEndpoint(os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT")),
+		otlptracehttp.WithInsecure(),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	tp := sdktrace.NewTracerProvider(
+		sdktrace.WithBatcher(exporter),
+		sdktrace.WithResource(resource.NewWithAttributes(
+			semconv.SchemaURL,
+			semconv.ServiceName(serviceName),
+		)),
+	)
+	otel.SetTracerProvider(tp)
+	return tp, nil
+}