Replace simple numbered menu with fzf fuzzy finder for dramatically
improved package selection experience.

## New Features

**fzf Integration:**
- Fuzzy search across all installed packages
- Multi-select with Tab key (select multiple packages at once)
- Live preview pane showing package details (type, name, version, size)
- Color-coded by package manager (APT=Blue, Snap=Magenta, Flatpak=Green, AppImage=Yellow)
- Auto-installs fzf if not present (via apt or GitHub)

**Enhanced UI:**
- Rounded border with styled header
- Real-time search as you type
- Preview pane (40% width) with package metadata
- Visual markers for selected packages (✓)
- Pointer indicator (▶) for current selection

**Improved Keyboard Navigation:**
- ↑↓ or j/k: Navigate list
- Tab: Toggle current selection
- Shift+Tab: Toggle + move up
- Ctrl+A: Select all packages
- Ctrl+D: Deselect all packages
- Enter: Confirm selection and proceed
- Esc: Cancel operation

**Performance Benefits:**
- Instant filtering with fuzzy matching
- No scrolling through hundreds of numbered items
- Can handle large package lists efficiently
- Type-ahead search finds packages instantly

## Implementation Details

**format_package_entry():**
- Formats each package with aligned columns
- Color codes by package type
- Shows: [TYPE] name version size

**ensure_fzf():**
- Checks if fzf is installed
- Auto-installs via apt-get if available
- Falls back to GitHub release if needed
- Adds to PATH automatically

**show_app_selector():**
- Prepares formatted display for fzf
- Configures fzf with custom theme and bindings
- Parses selections and returns raw package data
- Confirms before proceeding with uninstallation

## Updated Help & Banner

- Help message now documents fzf features
- Lists all keyboard shortcuts
- Banner indicates "(fzf)" integration
- Installation section mentions auto-install

## Backwards Compatibility

- Falls back gracefully if fzf installation fails
- All existing package scanning logic unchanged
- Same uninstall flow after selection
- System-critical and data-protected package checks intact

## Example Usage

```bash
$ fub uninstall

# Opens fzf interface:
# - Type "chrome" to filter to Chrome packages
# - Press Tab to select Google Chrome
# - Press Tab again to select Chromium
# - Press Enter to confirm
# - Confirm with 'y' to proceed
```

This upgrade makes uninstalling packages much faster and more intuitive,
especially on systems with many installed packages.