feat: add automatic version update checking and notifications

- Add internal/version module for GitHub release checking
- Integrate async version check in Bubble Tea UI
- Display update notification in main interface
- Add version check to --version/-v command output
- Include comprehensive version comparison and error handling
- Add unit tests for version parsing and comparison logic

internal/version/version_test.go

@@ -0,0 +1,56 @@
+package version
+
+import (
+	"testing"
+)
+
+func TestParseVersion(t *testing.T) {
+	tests := []struct {
+		version  string
+		expected []int
+	}{
+		{"v1.2.3", []int{1, 2, 3}},
+		{"1.2.3", []int{1, 2, 3}},
+		{"v2.0.0", []int{2, 0, 0}},
+		{"1.2.3-beta", []int{1, 2, 3}},
+		{"1.2.3-rc1", []int{1, 2, 3}},
+		{"dev", []int{0}},
+	}
+
+	for _, test := range tests {
+		result := parseVersion(test.version)
+		if len(result) != len(test.expected) {
+			t.Errorf("parseVersion(%q) length = %d, want %d", test.version, len(result), len(test.expected))
+			continue
+		}
+		for i, v := range result {
+			if v != test.expected[i] {
+				t.Errorf("parseVersion(%q)[%d] = %d, want %d", test.version, i, v, test.expected[i])
+				break
+			}
+		}
+	}
+}
+
+func TestCompareVersions(t *testing.T) {
+	tests := []struct {
+		v1       string
+		v2       string
+		expected int
+	}{
+		{"v1.0.0", "v1.0.1", -1},
+		{"v1.0.1", "v1.0.0", 1},
+		{"v1.0.0", "v1.0.0", 0},
+		{"1.2.3", "1.2.4", -1},
+		{"2.0.0", "1.9.9", 1},
+		{"1.2.3-beta", "1.2.3", 0}, // Should ignore suffixes
+		{"1.2.3", "1.2.3-rc1", 0},
+	}
+
+	for _, test := range tests {
+		result := compareVersions(test.v1, test.v2)
+		if result != test.expected {
+			t.Errorf("compareVersions(%q, %q) = %d, want %d", test.v1, test.v2, result, test.expected)
+		}
+	}
+}