feat: rewrite gh-commit in Go with local Ollama backend

Replaces the Python/Crush/DuckDB implementation with a CGO-free Go binary:
cobra CLI, modernc.org/sqlite storage, huh/lipgloss UI, and speed-tuned raw
/api/generate calls (think:false, keep_alive, capped num_predict) against a
local qwen3.5:2b. Ships as a gh extension via cli/gh-extension-precompile.

internal/gitx/git_test.go

@@ -0,0 +1,74 @@
+package gitx
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func TestFilesInScope(t *testing.T) {
+	files := []string{
+		"cmd/root.go",
+		"cmd/list.go",
+		"internal/db/store.go",
+		"README.md",
+		"cmdlets/x.go",
+	}
+	tests := []struct {
+		name     string
+		prefixes []string
+		want     []string
+	}{
+		{"directory prefix", []string{"cmd/"}, []string{"cmd/root.go", "cmd/list.go"}},
+		{"bare prefix matches sibling dirs too", []string{"cmd"}, []string{"cmd/root.go", "cmd/list.go", "cmdlets/x.go"}},
+		{"exact file", []string{"README.md"}, []string{"README.md"}},
+		{"multiple prefixes no duplicates", []string{"cmd/", "cmd/root"}, []string{"cmd/root.go", "cmd/list.go"}},
+		{"no match", []string{"docs/"}, nil},
+		{"empty prefixes", nil, nil},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := FilesInScope(files, tt.prefixes); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("got %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestGitignoreHash(t *testing.T) {
+	dir := t.TempDir()
+
+	if got := GitignoreHash(dir); got != "" {
+		t.Errorf("missing .gitignore should hash to empty string, got %q", got)
+	}
+
+	path := filepath.Join(dir, ".gitignore")
+	if err := os.WriteFile(path, []byte("node_modules/\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	// sha256 of "node_modules/\n"
+	first := GitignoreHash(dir)
+	if len(first) != 64 {
+		t.Errorf("want 64-char hex digest, got %q", first)
+	}
+	if again := GitignoreHash(dir); again != first {
+		t.Error("hash must be deterministic")
+	}
+
+	if err := os.WriteFile(path, []byte("dist/\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if changed := GitignoreHash(dir); changed == first {
+		t.Error("hash must change when content changes")
+	}
+}
+
+func TestLines(t *testing.T) {
+	if got := Lines("a\n\nb\n"); !reflect.DeepEqual(got, []string{"a", "b"}) {
+		t.Errorf("got %v", got)
+	}
+	if got := Lines(""); got != nil {
+		t.Errorf("empty output should yield nil, got %v", got)
+	}
+}