feat(httpclient): initial stable release v0.9.0

Resilient HTTP client with circuit breaking, exponential-backoff retry, X-Request-ID propagation, and a generic typed JSON helper.

What's included:
- Client interface with Do(req) method; New(logger, cfg) and NewWithDefaults(logger) constructors
- Config struct with env-tag support for timeout, dial timeout, retry, and circuit breaker parameters
- Retry via avast/retry-go/v4 with BackOffDelay; triggers only on network errors and HTTP 5xx
- Circuit breaker via sony/gobreaker wrapping the full retry loop; open circuit → xerrors.ErrUnavailable
- X-Request-ID header propagated automatically from context via logz.GetRequestID on every attempt
- DoJSON[T](ctx, client, req) generic helper for typed JSON request/response with xerrors error mapping
- MapStatusToError(code, msg) exported function mapping HTTP status codes to xerrors types

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

doc.go

@@ -0,0 +1,10 @@
+// Package httpclient provides a resilient HTTP client with automatic retry and circuit breaking.
+//
+// Usage:
+//
+//	client := httpclient.NewWithDefaults(logger)
+//	resp, err := client.Do(req)
+//
+//	// Typed JSON helper
+//	order, err := httpclient.DoJSON[Order](ctx, client, req)
+package httpclient