fix: capture exception details for 500/405 responses with empty body

[algojogacor]

Summary

Fixes #36 — When unhandled exceptions occur, DebugProbe showed the response as having status code 500 but with an empty response body, making debugging difficult.

Root Cause

The middleware's try/catch/finally pattern intercepts the response stream via MemoryStream. When await _next(context) throws:

1. The exception is caught and re-thrown
2. The finally block reads the MemoryStream — but at this point ASP.NET Core's exception handling middleware hasn't written anything to it yet
3. Result: stored response body is empty

Solution

Added two fields to DebugEntry and capture exception data in the catch block:

• ExceptionMessage — the exception's .Message
• ExceptionStackTrace — the exception's .StackTrace (trimmed to 4000 chars for readability)

This ensures that even when the response body hasn't been written yet by downstream middleware, the DebugProbe UI can display the actual exception that occurred.

Changes

File	Change
DebugProbe.AspNetCore/Models/DebugEntry.cs	Add ExceptionMessage and ExceptionStackTrace properties
DebugProbe.AspNetCore/Middleware/DebugProbeMiddleware.cs	Capture exception details in catch block; increase stack trace trim limit to 4000

Testing

• Trigger an unhandled exception → verify ExceptionMessage/StackTrace appear in DebugProbe UI
• Normal successful requests → verify ExceptionMessage/StackTrace are null (no regression)
• Build passes

[georgidhristov]

Tested locally. The backend exception capture works correctly and fixes the empty response debugging issue.

The UI currently still shows an empty response body because ExceptionMessage/ExceptionStackTrace are not rendered yet. I will handle the UI support separately in another issue/PR.

Thanks for the contribution.