fix(host): pass HttpClient to EspoCrmClient ctor + dispose on shutdown

The composition root was calling EspoCrmClient(baseUrl, user, key, logger)
which doesn't match the actual ctor signature
EspoCrmClient(HttpClient, string, string, string, ILogger). One missing
HttpClient argument = one compile error blocking the host build.

- AddInHost now owns a single HttpClient (Timeout=30s), passed to
  EspoCrmClient on init, disposed alongside the retry processor and
  Serilog on shutdown.
- baseUrl.ToString() satisfies the string parameter; the Uri.TryCreate
  upstream still validates the URL.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/OutlookAddin/Services/AddInHost.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Http;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using System.Windows;
@@ -36,6 +37,7 @@ namespace OutlookAddin.Services
 
         private readonly Outlook.Application _outlookApp;
         private RetryQueueProcessor? _retryProcessor;
+        private HttpClient? _httpClient;
 
         public AddInHost(Outlook.Application outlookApp)
         {
@@ -70,7 +72,8 @@ namespace OutlookAddin.Services
 
             try
             {
-                CrmClient = new EspoCrmClient(baseUrl, creds.Username, creds.ApiKey, Logger);
+                _httpClient = new HttpClient { Timeout = TimeSpan.FromSeconds(30) };
+                CrmClient = new EspoCrmClient(_httpClient, baseUrl.ToString(), creds.Username, creds.ApiKey, Logger);
                 FilingService = new FilingService(CrmClient, RetryQueue, Logger);
                 _retryProcessor = new RetryQueueProcessor(RetryQueue, CrmClient, Logger);
                 _retryProcessor.Start();
@@ -318,6 +321,7 @@ namespace OutlookAddin.Services
         public void Dispose()
         {
             try { _retryProcessor?.Dispose(); } catch { }
+            try { _httpClient?.Dispose(); } catch { }
             try
             {
                 Logger.Information("AddInHost shutting down");