feat: complete Rust-to-Go rewrite with Bubbletea v2

Rewrites oxker from Rust/ratatui to Go/Bubbletea, migrated to the
Bubbletea v2 API (charm.land/bubbletea/v2). Removes all original Rust
source files and legacy Go modules (internal/ui, internal/input, bubbles).

Key changes:
- View() returns tea.View with declarative AltScreen and MouseMode
- KeyMsg → KeyPressMsg, MouseMsg → MouseClickMsg/WheelMsg/MotionMsg/ReleaseMsg
- execWriteKey rewritten for v2 key fields (Code/Mod/Text)
- Mouse toggle via View field instead of imperative commands
- Filter/search text input uses msg.Text for v2 space key compat

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/utils/scroll.go

@@ -0,0 +1,31 @@
+package utils
+
+type ScrollDirection int
+
+const (
+	ScrollUp ScrollDirection = iota
+	ScrollDown
+	ScrollPageUp
+	ScrollPageDown
+	ScrollHome
+	ScrollEnd
+)
+
+func (sd ScrollDirection) String() string {
+	switch sd {
+	case ScrollUp:
+		return "up"
+	case ScrollDown:
+		return "down"
+	case ScrollPageUp:
+		return "pageup"
+	case ScrollPageDown:
+		return "pagedown"
+	case ScrollHome:
+		return "home"
+	case ScrollEnd:
+		return "end"
+	default:
+		return "unknown"
+	}
+}