MFR client: align with interface doc; remove VB-era files

Per MFR_RESTClient/Docs/mfr_interface_description.md (added):
- MFRClientConfig: configurable TimeoutMs (default 30000), UserAgent, MaxRetries,
  and a derived RestRoot (/mfr) alongside the OData BaseUrl.
- MFRClient: apply request Timeout + UserAgent, send Accept: application/json,
  and retry idempotent GETs on transient failures (HTTP 429/5xx and
  network/timeout) with exponential backoff + jitter, honouring Retry-After.
- Added ReadODataAllPages to follow @odata.nextLink pagination.

Cleanup: removed legacy VB project files (MFR_RESTClient.vbproj, .vbproj.user,
app.config My.MySettings) and stopped tracking the generated MFR_RESTClient.xml
(now git-ignored). The active project is MFR_RESTClient.csproj.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -11,6 +11,9 @@ obj/
 *.dbmdl
 *.jfm
 
+# Generated XML documentation output (regenerated on build)
+MFR_RESTClient/MFR_RESTClient.xml
+
 # NuGet
 packages/
 *.nupkg