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

internal/route/rules/io.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/yusing/godoxy/internal/common"
 	"github.com/yusing/godoxy/internal/logging/accesslog"
+	gperr "github.com/yusing/goutils/errs"
 )
 
 type noopWriteCloser struct {
@@ -30,7 +31,7 @@ var (
 	testFilesLock sync.Mutex
 )
 
-func openFile(path string) (io.WriteCloser, error) {
+func openFile(path string) (io.WriteCloser, gperr.Error) {
 	switch path {
 	case "/dev/stdout":
 		return stdout, nil