Prevent stuck positronHelpFocused context key from hijacking copy

[juliasilge]

Addresses the part of #9364 that is about Positron Help focus, not about the upstream problem

The positronHelpFocused context key can apparently sometimes get stuck at true when the Help webview's onDidBlur event fails to fire (pane collapse, release() with retainContextWhenHidden, iframe navigation races). With the key stuck true, Cmd/Ctrl+C resolved to positron.help.copy instead of the normal copy command. This breaks user copy/paste anywhere in the workbench until a new help page was loaded to "jiggle" the focus cycle back into alignment. I still have not been able to reproduce the problem myself, so the changes in this PR are somewhat speculative.

The PR does two things:

• Defensively clears positronHelpFocused to false in HelpEntry.dispose() and HelpEntry.hideHelpOverlayWebview(), independent of whether the webview fires blur.
• Routes all writes to the context key through a small helper that logs transitions via ILogService, tagged [positronHelpFocused]. Logs land in the Window output channel and are captured in diagnostic reports. If people still have trouble moving forward, we can hopefully diagnose the underlying root cause a bit better moving forward.

A follow-up could switch the focus tracking to DOM.trackFocus() on the Help container (the pattern the Console
uses) to eliminate the failure mode entirely but this PR is just a minimal mitigation plus the data we'd need to justify a larger change.

Release Notes

New Features

• N/A

Bug Fixes

• Prevent the Help copy keybinding from hijacking Cmd/Ctrl+C elsewhere in the app when Help focus tracking misses a blur event (Keyboard shortcut for "Copy" fails randomly #9364)

QA Notes

@:help @:web @:win

1. Open Positron with an R or Python session.
2. Run ?lm (R) or help(print) (Python). Confirm the help page renders in the Help pane.
3. Click into the help body so it has keyboard focus.
4. Click into the console, select some text, and press Cmd/Ctrl+C. Confirm the text is copied (not hijacked by the Help copy command).
5. Open View → Output → Window and look for [positronHelpFocused] lines on focus transitions, e.g., "webview.onDidFocus: false -> true" and "webview.onDidBlur: true -> false".
6. Collapse the Help pane while it's focused, then re-expand it. Confirm help still renders, Cmd/Ctrl+C still works elsewhere, and the log shows a "hideHelpOverlayWebview(dispose=false): true -> false" transition.
7. Navigate between help topics (e.g., ?lm then ?glm). Confirm each entry renders and logs show clean focus/blur cycles.

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical @:help @:web @:win

^{readme  valid tags}