release: prepare v1.0.0-alpha1 release

- Set version to 1.0.0-alpha1 for initial release under new package name
- Update UserAgent to include full version number (1.0.0-alpha1)
- Update release notes to reflect initial alpha release of Reliable.HttpClient

This prepares the project for publishing as the first alpha version
of the renamed package (previously HttpClient.Resilience).

Author: akrisanov

src/Reliable.HttpClient/HttpClientOptions.cs

@@ -18,7 +18,7 @@ public class HttpClientOptions
     /// <summary>
     /// User-Agent for HTTP requests
     /// </summary>
-    public string UserAgent { get; set; } = "Reliable.HttpClient/1.0";
+    public string UserAgent { get; set; } = "Reliable.HttpClient/1.0.0-alpha1";
 
     /// <summary>
     /// Retry policy configuration

src/Reliable.HttpClient/Reliable.HttpClient.csproj

@@ -3,10 +3,11 @@
     <TargetFrameworks>net6.0;net8.0;net9.0</TargetFrameworks>
     <AssemblyName>Reliable.HttpClient</AssemblyName>
     <PackageId>Reliable.HttpClient</PackageId>
-    <Version>1.0.0-alpha3</Version>
-    <PackageReleaseNotes>Added configuration validation, performance improvements with specific
-      return types,
-      and suppressed .NET 6.0 compatibility warnings.</PackageReleaseNotes>
+    <Version>1.0.0-alpha1</Version>
+    <PackageReleaseNotes>Initial alpha release of Reliable.HttpClient (renamed from
+      HttpClient.Resilience).
+      Features: retry with exponential backoff and jitter, circuit breaker, and HTTP response
+      handling.</PackageReleaseNotes>
     <Authors>Andrey Krisanov</Authors>
     <Company></Company>
     <Description>Lightweight resilience helpers (retry with jitter, circuit breaker) and response