refactor: rewrite handler-base as Go module

Replace Python handler-base library with Go module providing:
- config: environment-based configuration
- health: HTTP health/readiness server for k8s probes
- natsutil: NATS/JetStream client with msgpack serialization
- telemetry: OpenTelemetry tracing and metrics setup
- clients: HTTP clients for LLM, embeddings, reranker, STT, TTS
- handler: base Handler runner wiring NATS + health + telemetry

Implements ADR-0061 Phase 1.

README.md

@@ -1,109 +1,44 @@
-# Handler Base
+# handler-base
 
-Shared base library for building NATS-based AI/ML handler services.
+Go module providing shared infrastructure for NATS-based handler services.
 
-## Installation
+## Packages
 
-```bash
-pip install handler-base
-```
+| Package | Purpose |
+|---------|---------|
+| `config` | Environment-based configuration via struct fields |
+| `health` | HTTP health/readiness server for Kubernetes probes |
+| `natsutil` | NATS/JetStream client with msgpack serialization |
+| `telemetry` | OpenTelemetry tracing and metrics setup |
+| `clients` | HTTP clients for LLM, embeddings, reranker, STT, TTS |
+| `handler` | Base Handler runner wiring NATS + health + telemetry |
 
-Or from Gitea:
-```bash
-pip install git+https://git.daviestechlabs.io/daviestechlabs/handler-base.git
-```
+## Usage
 
-## Quick Start
+```go
+package main
 
-```python
-from handler_base import Handler, Settings
-from nats.aio.msg import Msg
-
-class MyHandler(Handler):
-    async def setup(self):
-        # Initialize your clients
-        pass
-    
-    async def handle_message(self, msg: Msg, data: dict):
-        # Process the message
-        result = {"processed": True}
-        return result
-
-if __name__ == "__main__":
-    MyHandler(subject="my.subject").run()
-```
-
-## Features
-
-- **Handler base class** - NATS subscription, graceful shutdown, signal handling
-- **NATSClient** - Connection management, JetStream, msgpack serialization
-- **Settings** - Pydantic-based configuration from environment
-- **HealthServer** - Kubernetes liveness/readiness probes
-- **Telemetry** - OpenTelemetry tracing and metrics
-- **Service clients** - HTTP wrappers for AI services
-
-## Service Clients
-
-```python
-from handler_base.clients import (
-    STTClient,      # Whisper speech-to-text
-    TTSClient,      # XTTS text-to-speech
-    LLMClient,      # vLLM chat completions
-    EmbeddingsClient,  # BGE embeddings
-    RerankerClient,    # BGE reranker
-    MilvusClient,      # Vector database
+import (
+    "context"
+    "git.daviestechlabs.io/daviestechlabs/handler-base/config"
+    "git.daviestechlabs.io/daviestechlabs/handler-base/handler"
+    "github.com/nats-io/nats.go"
 )
+
+func main() {
+    cfg := config.Load()
+    cfg.ServiceName = "my-service"
+
+    h := handler.New("my.subject", cfg)
+    h.OnMessage(func(ctx context.Context, msg *nats.Msg, data map[string]any) (map[string]any, error) {
+        return map[string]any{"ok": true}, nil
+    })
+    h.Run()
+}
 ```
 
-## Configuration
+## Testing
 
-All settings via environment variables:
-
-| Variable | Default | Description |
-|----------|---------|-------------|
-| `NATS_URL` | `nats://localhost:4222` | NATS server URL |
-| `NATS_USER` | - | NATS username |
-| `NATS_PASSWORD` | - | NATS password |
-| `NATS_QUEUE_GROUP` | - | Queue group for load balancing |
-| `HEALTH_PORT` | `8080` | Health check server port |
-| `OTEL_ENABLED` | `true` | Enable OpenTelemetry |
-| `OTEL_EXPORTER_OTLP_ENDPOINT` | `http://localhost:4317` | OTLP endpoint |
-| `OTEL_SERVICE_NAME` | `handler` | Service name for traces |
-
-## Docker
-
-```dockerfile
-FROM ghcr.io/daviestechlabs/handler-base:latest
-
-COPY my_handler.py /app/
-CMD ["python", "/app/my_handler.py"]
-```
-
-Or build with audio support:
 ```bash
-docker build --build-arg INSTALL_AUDIO=true -t my-handler .
+go test ./...
 ```
-
-## Module Structure
-
-```
-handler_base/
-├── __init__.py      # Public API exports
-├── handler.py       # Base Handler class
-├── nats_client.py   # NATS connection wrapper
-├── config.py        # Pydantic Settings
-├── health.py        # Health check server
-├── telemetry.py     # OpenTelemetry setup
-└── clients/
-    ├── embeddings.py
-    ├── llm.py
-    ├── milvus.py
-    ├── reranker.py
-    ├── stt.py
-    └── tts.py
-```
-
-## Related
-
-- [voice-assistant](https://git.daviestechlabs.io/daviestechlabs/voice-assistant) - Voice pipeline using handler-base
-- [homelab-design](https://git.daviestechlabs.io/daviestechlabs/homelab-design) - Architecture docs