feat : allow taking a screenshot for bug reports (#1678)

This PR implements allowing users to take a screenshot for bug reports
and addresses issue #1125









<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Adds screenshot capture to bug reports. Users can take a screenshot
that’s copied to the clipboard, then continue to file the issue.

- **New Features**
  - New BugScreenshotDialog to take a screenshot or report without one.
- ScreenshotSuccessDialog confirms capture and guides users to the
GitHub issue.
- HelpDialog now opens the screenshot flow; issue template includes an
optional Screenshot section.
- Electron IPC handler take-screenshot captures the focused window and
writes the image to the clipboard; exposed via IpcClient and whitelisted
in preload.

<sup>Written for commit de0f9b059ae508b56c3c46664559eead3dffa413.
Summary will update automatically on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

src/preload.ts

@@ -121,6 +121,8 @@ const validInvokeChannels = [
   "mcp:set-tool-consent",
   // MCP consent response from renderer to main
   "mcp:tool-consent-response",
+  // Help
+  "take-screenshot",
   // Help bot
   "help:chat:start",
   "help:chat:cancel",