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>

build.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# Build script for Oxker Go TUI
+# This script builds the Go application
+
+set -e
+
+cd "$(dirname "$0")"
+
+echo "Building Oxker..."
+go build -o oxker ./cmd/oxker
+echo "Build complete: ./oxker"
+
+echo "Running go vet..."
+go vet ./...
+
+echo "Running go mod tidy..."
+go mod tidy