[anton-gor-dev]

Summary

• Vue DevTools renders a built-in search box for custom inspectors and forwards the typed query as payload.filter in the getInspectorTree hook — but the plugin's handler (packages/plugin/src/vue/devtools/index.ts) ignored it entirely, so typing in the search box had no effect on any of the three composable inspectors.
• Added filterTree, which recursively filters a built tree by matching node label (case-insensitively): a node is kept if it matches directly (in which case all of its children are kept too, for context) or if any of its descendants match (in which case only the matching descendants are kept).
• Wired filterTree into getInspectorTree so payload.filter is applied to the tree before it's sent to DevTools, and added a treeFilterPlaceholder to each inspector so the search box hints at what can be searched.

Closes #27

Test plan

• pnpm vitest run packages/plugin passes (added unit tests for filterTree)
• pnpm lint passes
• pnpm plugin:build succeeds