Desktop search opens replies without parent thread or channel context

## Summary

Opening a message result from Desktop search can strand the user in an isolated nested-branch view instead of showing where the message belongs.

The panel displays only the matched reply and ends with:

> No replies in this branch yet
> Reply in thread to continue this branch

There is no visible originating channel message, no highlighted match in its parent conversation, no parent/root breadcrumb, and no action to open the complete parent thread. The composer consequently encourages the user to create another nested branch without making that consequence clear.

## Steps to reproduce

1. In Buzz Desktop, search for text contained in a reply inside an existing channel thread.
2. Open the matching message result.
3. Observe the thread panel.

## Actual behavior

- The matched reply is opened as an isolated branch root.
- The originating channel/root message is not visible or highlighted.
- Earlier thread context is absent.
- No channel → root thread → matched reply breadcrumb is shown.
- There is no **Open parent thread** or **Back to channel message** action.
- The empty-branch composer invites a reply that would create another nested branch.

This makes a successfully found message practically unusable for recovering and continuing a conversation.

## Expected behavior

Opening a message search result should preserve conversation context:

- open the complete parent/root thread;
- scroll to and visibly highlight the matched message;
- identify the originating channel and root message;
- provide explicit **Open parent thread** and/or **Back to channel** navigation;
- avoid presenting an empty nested-branch composer as though it were the recovered conversation.

If an isolated-branch view remains supported, it should clearly expose its parent chain and offer a one-click route to the root conversation.

## Acceptance criteria

- [ ] Opening a reply from search exposes the originating channel and root thread.
- [ ] The matched message is scrolled into view and visibly highlighted.
- [ ] The user can navigate directly to the parent/root conversation.
- [ ] The UI clearly distinguishes replying to the matched message from continuing the root thread.
- [ ] Search results for top-level messages, root messages, direct replies, and nested replies have automated navigation coverage.

## Related issues checked

- #2853 concerns search operators, not result navigation.
- #3799 concerns replies missing from a thread view, not loss of context when opening search results.
- #47 introduced nested threads but does not track this navigation failure.

Reproduce the issue in Buzz Desktop by opening a reply from search, then trace the search-result navigation into the thread panel. Check the existing navigation for top-level messages, root messages, direct replies, and nested replies, and add automated coverage so the parent context, matched-message highlight, and root navigation are present without misleading branch-reply behavior.

Written by the indexing model from the issue text.