feat: Implement configuration management and DNS provider integration

- Added configuration management using Viper in internal/config/config.go
- Implemented ClientConfig, ServerConfig, TLSConfig, HetznerConfig, UpstreamConfig, and main Config struct.
- Created LoadConfig function to read and validate configuration files.
- Developed Hetzner DNS provider in internal/provider/hetzner/hetzner.go with methods for updating DNS records.
- Added comprehensive unit tests for configuration loading and Hetzner provider functionality.
- Established HTTP server with metrics and update endpoint in internal/server/server.go.
- Implemented request handling, authorization, and error management in the server.
- Created integration tests for the Hetzner provider API interactions.
- Removed legacy dynamic DNS integration tests in favor of the new API-based approach.

development-plan.md

@@ -0,0 +1,146 @@
+# Development Plan for UpDNS
+
+A step-by-step roadmap to build, test, and evolve the Go‑based DynDNS proxy—including support for both exact hostnames and wildcard domains.
+
+---
+
+## Phase 1: Project Setup (Week 1)
+
+1. **Repository Initialization**
+   - `go mod init git.cloonar.com/cloonar/updns`
+   - Create directory structure:
+     ```
+     cmd/updns
+     internal/config
+     internal/server
+     internal/provider
+     test/
+     ```
+
+2. **Configuration Loader**
+   - Use [spf13/viper] to parse YAML/JSON/TOML.
+   - Define `Config` struct with:
+     ```go
+     type ClientConfig struct {
+       Secret   string   `mapstructure:"secret"`
+       Exact    []string `mapstructure:"exact"`
+       Wildcard []string `mapstructure:"wildcard"`
+     }
+
+     type Config struct {
+       Server   ServerConfig             `mapstructure:"server"`
+       Upstream UpstreamConfig           `mapstructure:"upstream"`
+       Clients  map[string]ClientConfig  `mapstructure:"clients"`
+     }
+     ```
+   - Validate that at least one of `Exact` or `Wildcard` is set per client.
+
+3. **Main & CLI**
+   - Parse `--config` flag.
+   - Load config, handle errors, and pass into server setup.
+
+---
+
+## Phase 2: HTTP API & Authentication (Week 2)
+
+1. **Server Implementation**
+   - Choose router: `net/http` or `gin-gonic/gin`.
+   - Define route `POST /update`.
+
+2. **Authentication & Authorization**
+   - Middleware to:
+     - Lookup client by `key`.
+     - Verify `secret` matches stored token.
+     - Check that requested `host` is allowed by matching either:
+       - An entry in `Exact` (full string equality), or
+       - A wildcard base domain in `Wildcard`, e.g. `example.com` matches `foo.example.com` and `example.com`.
+   - Reject requests with clear error if host not authorized.
+
+3. **Request Validation**
+   - Validate JSON payload: `key`, `secret`, `host`, optional `ip`.
+   - Default `ip` to requestor’s IP if omitted.
+
+---
+
+## Phase 3: Hetzner Provider Integration (Week 3)
+
+1. **Provider Interface**  
+   ```go
+   type Provider interface {
+     UpdateRecord(ctx context.Context, domain, ip string) error
+   }
+   ```
+
+2. **Hetzner Implementation**
+   - On startup, fetch or cache record IDs by domain.
+   - Use Hetzner’s DDNS API to PATCH IP on update.
+
+3. **Error Handling & Retries**
+   - Retry transient errors with exponential backoff.
+   - Surface permanent errors in response.
+
+---
+
+## Phase 4: Testing & CI (Week 4)
+
+1. **Unit Tests**
+   - Config parsing, ensuring `Exact` and `Wildcard` fields load correctly.
+   - Authorization logic: hosts matching exact list vs. wildcard list.
+   - Secret validation.
+
+2. **Integration Tests**
+   - Use `httptest.Server` to simulate upstream.
+   - Test success and failure for:
+     - Exact hostname updates.
+     - Subdomain updates via wildcard rules.
+     - Unauthorized host attempts.
+
+3. **CI Pipeline**
+   - GitHub Actions to run `go fmt`, `go vet`, `go test`.
+   - Build artifacts for Linux/macOS.
+
+---
+
+## Phase 5: TLS, Logging & Metrics (Week 5)
+
+1. **TLS Support**
+   - Enable HTTPS when `tls.enabled` in config.
+   - Load cert/key files.
+
+2. **Structured Logging**
+   - Integrate `uber/zap` or `sirupsen/logrus`.
+   - Log requests, responses, errors, and authorization decisions (with no secrets).
+
+3. **Metrics**
+   - Expose Prometheus `/metrics` endpoint.
+   - Track:
+     - Total updates.
+     - Successes vs. failures.
+     - Requests authorized via exact vs. wildcard.
+
+---
+
+## Phase 6: Extensibility & Additional Providers (Week 6)
+
+1. **Provider Factory**
+   - Map `upstream.provider` string to constructor.
+
+2. **Cloudflare & AWS Stubs**
+   - Scaffold `cloudflare` and `aws` provider packages.
+   - Document config for each.
+
+3. **Documentation Update**
+   - Update README to reflect exact + wildcard support and new provider instructions.
+
+---
+
+## Phase 7: Deployment & Release (Week 7)
+
+1. **Dockerization**
+   - Write `Dockerfile` and example `docker-compose.yml`.
+
+2. **Optional Helm Chart**
+   - Package for Kubernetes.
+
+3. **Release v1.0.0**
+   - Tag in GitHub, attach binaries, update changelog.