Fixed help overlay scrolling, plus search wording and README cleanup

Highlights

• Fixed the help overlay being cut off on smaller terminals -
  it now scrolls with j/k and dims the background while open
• Renamed "filter" to "search" throughout the UI and docs,
  since that's what it actually does - look things up by name,
  description, or category
• Search bar now shows a placeholder and cursor when active
• Empty search results show a hint to press Esc to clear them
• Replaced the yellow input-mode color with a cyan-adjacent tone
• README overhaul: corrected keybindings, added category
  management docs, installation via releases, and a screenshot

categories, status feedback, and a reorganized Details pane

v0.9.1

Categories

• Add category creation, rename, and deletion workflow
• Mark packages with Space and move them into a category
  from the Categories pane
• Reject duplicate and reserved category names
• Format-preserving category file edits (via toml_edit),
  so categories.toml keeps its formatting on save

Status & feedback

• New status message system for action feedback (create,
  rename, delete, move)
• Statusbar now right-aligns status messages instead of
  replacing keybind hints, and drops hints gracefully on
  narrow terminals

Details pane

• Reorganized into Package / Dependencies / Files sections,
  matching pacman -Qi's field ordering
• Long dependency/license lists now show a count instead of
  an unbroken wall of text
• New: Install Script field
• Package title now shows an icon, version, and description
  at a glance

Fixes

• Fixed duplicate "Uncategorized" category
• Fixed package-list mark-column truncation