Initial BinaryLane v2 API client

docs/errors.md

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+# Error handling
+
+All API failures derive from `BinaryLaneApiException`.
+
+| Exception | When it is used |
+| --- | --- |
+| `BinaryLaneUnauthorizedException` | The token is missing, invalid, or expired. |
+| `BinaryLaneForbiddenException` | The token does not have access to the resource. |
+| `BinaryLaneNotFoundException` | The requested resource does not exist or is not visible to the token. |
+| `BinaryLaneValidationException` | BinaryLane rejected the request payload. |
+| `BinaryLaneApiException` | Any other non-success HTTP response. |
+
+```csharp
+using BinaryLane.Api.V2.Errors;
+
+try
+{
+    var server = await client.Servers.GetAsync(serverId, cancellationToken);
+}
+catch (BinaryLaneNotFoundException)
+{
+    // Handle a missing server.
+}
+catch (BinaryLaneValidationException)
+{
+    // Show an appropriate validation message to the caller.
+}
+catch (BinaryLaneApiException exception)
+{
+    // Use exception.StatusCode to choose an application-specific response.
+}
+```
+
+Each exception provides `StatusCode`, `RequestUri`, `Headers`, and, when
+available, `Problem` and `ResponseBody`. Provider detail text can contain user
+data. Do not write `Problem`, `Headers`, or `ResponseBody` to application logs
+without appropriate redaction.
+
+Successful JSON responses are limited to 16 MiB. A larger response throws
+`HttpRequestException` before the client buffers it in memory.