feat(rules): introduce block DSL, phase-based execution (#203)

* chore(deps): update submodule goutils

* docs(http): remove default client from README.md

* refactor(rules): introduce block DSL, phase-based execution, and flow validation

- add block syntax parser/scanner with nested @blocks and elif/else support
- restructure rule execution into explicit pre/post phases with phase flags
- classify commands by phase and termination behavior
- enforce flow semantics (default rule handling, dead-rule detection)
- expand HTTP flow coverage with block + YAML parity tests and benches
- refresh rules README/spec and update playground/docs integration
- Default rules act as fallback handlers that execute only when no matching non-default rule exists in the pre phase
- IfElseBlockCommand now returns early when a condition matches with a nil Do block, instead of falling through to else blocks
- Add nil check for auth handler to allow requests when no auth is configured

* fix(rules): buffer log output before writing to stdout/stderr

* refactor(api/rules): remove IsResponseRule field from ParsedRule and related logic

* docs(rules): update examples to use block syntax

internal/route/rules/do_blocks_test.go

@@ -0,0 +1,73 @@
+package rules
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	httputils "github.com/yusing/goutils/http"
+)
+
+func TestIfElseBlockCommandServeHTTP_UnconditionalNilDoNotFallsThrough(t *testing.T) {
+	elseCalled := false
+	cmd := IfElseBlockCommand{
+		Ifs: []IfBlockCommand{
+			{
+				On: RuleOn{},
+				Do: nil,
+			},
+		},
+		Else: []CommandHandler{
+			Handler{
+				fn: func(_ *httputils.ResponseModifier, _ *http.Request, _ http.HandlerFunc) error {
+					elseCalled = true
+					return nil
+				},
+				phase: PhaseNone,
+			},
+		},
+	}
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	w := httptest.NewRecorder()
+	rm := httputils.NewResponseModifier(w)
+
+	err := cmd.ServeHTTP(rm, req, nil)
+	require.NoError(t, err)
+	assert.False(t, elseCalled)
+}
+
+func TestIfElseBlockCommandServeHTTP_ConditionalMatchedNilDoNotFallsThrough(t *testing.T) {
+	elseCalled := false
+	cmd := IfElseBlockCommand{
+		Ifs: []IfBlockCommand{
+			{
+				On: RuleOn{
+					checker: CheckFunc(func(_ *httputils.ResponseModifier, _ *http.Request) bool {
+						return true
+					}),
+				},
+				Do: nil,
+			},
+		},
+		Else: []CommandHandler{
+			Handler{
+				fn: func(_ *httputils.ResponseModifier, _ *http.Request, _ http.HandlerFunc) error {
+					elseCalled = true
+					return nil
+				},
+				phase: PhaseNone,
+			},
+		},
+	}
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	w := httptest.NewRecorder()
+	rm := httputils.NewResponseModifier(w)
+
+	err := cmd.ServeHTTP(rm, req, nil)
+	require.NoError(t, err)
+	assert.False(t, elseCalled)
+}