feat(frontend): knowledge base full-text search result viewer

[mrveiss]

Summary

KnowledgeManager.vue:1342 has a TODO for a KB search result viewer. Search results are returned from the backend but there is no UI to display them inline — results are currently lost.

Implementation

• Create a KBSearchResultPanel component showing ranked results with title, snippet, and source
• Open result documents in a read-only viewer pane
• Support keyboard navigation through results
• Highlight matching terms in snippets

Acceptance criteria

• Search results display with title, relevance score, and snippet
• Clicking a result opens the full document in a viewer
• Matched terms are highlighted in the snippet
• Keyboard navigation (arrow keys, Enter, Escape) works