Implement search

This is a request to implement a search which will search a substring from keys and values.

It would maybe limit the tree view to view only the matching keys (and the parent keys).

No files or tests are named in the issue. Start by locating the tree-view entry point in the development tool, then trace how keys and values are rendered. Done means a substring search can limit the tree to matching keys or values while retaining their parent keys; the exact interaction and empty-result behavior still need clarification.

Written by the indexing model from the issue text.