Add Text Search

  ## Description
  Add traditional keyword-based text search for clipboard history.

  ## Tasks
  - [ ] Add search input component in UI
  - [ ] Implement fuzzy/substring matching
  - [ ] Highlight matching text in results
  - [ ] Show "no results" state
  - [ ] Add clear search button

  ## Technical Details
  - Case-insensitive search
  - Filter clipboard history array by search term