feat(lsp): add textDocument/rangeFormatting support

Advertise DocumentRangeFormattingProvider in server capabilities and
implement rangeFormat: formats the complete document, then returns an
edit covering only the minimal changed-line region that overlaps the
client's selection. Also includes gofmt alignment fixes across lint
and format packages.

pkg/lsp/server_test.go

@@ -156,6 +156,76 @@ func TestFormatting(t *testing.T) {
 	}
 }
 
+func TestRangeFormatting(t *testing.T) {
+	// Two statements: first is unformatted, second is already formatted.
+	// Range request covers only the first statement (line 0).
+	sql := "select a, b from t where x = 1;\nSELECT z\nFROM s;\n"
+	uri := "file:///range.sql"
+
+	var input []byte
+	input = append(input, frame(1, "initialize", map[string]interface{}{})...)
+	input = append(input, notifFrame("initialized", nil)...)
+	input = append(input, notifFrame("textDocument/didOpen", map[string]interface{}{
+		"textDocument": map[string]interface{}{
+			"uri": uri, "languageId": "sql", "version": 1, "text": sql,
+		},
+	})...)
+	input = append(input, frame(2, "textDocument/rangeFormatting", map[string]interface{}{
+		"textDocument": map[string]interface{}{"uri": uri},
+		"range": map[string]interface{}{
+			"start": map[string]interface{}{"line": 0, "character": 0},
+			"end":   map[string]interface{}{"line": 0, "character": 31},
+		},
+		"options": map[string]interface{}{"tabSize": 2, "insertSpaces": true},
+	})...)
+	input = append(input, frame(3, "shutdown", nil)...)
+	input = append(input, notifFrame("exit", nil)...)
+
+	out := runServer(t, input)
+
+	var resp map[string]interface{}
+	for i := 0; i < 10; i++ {
+		r := readResp(t, out)
+		if r == nil {
+			break
+		}
+		if id, ok := r["id"]; ok && id.(float64) == 2 {
+			resp = r
+			break
+		}
+	}
+	if resp == nil {
+		t.Fatal("no response for rangeFormatting request")
+	}
+	result, ok := resp["result"].([]interface{})
+	if !ok || len(result) == 0 {
+		t.Fatalf("expected non-empty edit array, got %v", resp["result"])
+	}
+	edit := result[0].(map[string]interface{})
+	newText, _ := edit["newText"].(string)
+	if !strings.Contains(newText, "SELECT") {
+		t.Errorf("expected formatted SELECT in edit, got: %q", newText)
+	}
+	if strings.Contains(newText, "SELECT z") {
+		t.Errorf("range formatting edited second statement unexpectedly; got: %q", newText)
+	}
+}
+
+func TestInitialize_AdvertisesRangeFormatting(t *testing.T) {
+	input := append(frame(1, "initialize", map[string]interface{}{}),
+		notifFrame("initialized", map[string]interface{}{})...)
+	input = append(input, frame(2, "shutdown", nil)...)
+	input = append(input, notifFrame("exit", nil)...)
+
+	out := runServer(t, input)
+
+	resp := readResp(t, out)
+	caps := resp["result"].(map[string]interface{})["capabilities"].(map[string]interface{})
+	if caps["documentRangeFormattingProvider"] != true {
+		t.Error("expected documentRangeFormattingProvider=true")
+	}
+}
+
 func TestDidClose_ClearsDiagnostics(t *testing.T) {
 	uri := "file:///test.sql"
 	// SQL with a lint violation (SELECT * triggers COR001)