fix(process): AX-6 banned-import purge in program.go (#299)

Replaced bytes/strings/unicode imports with core.NewBuffer, core.* helpers,
and core.IsLetter / core.IsDigit. No banned imports remain.

Closes tasks.lthn.sh/view.php?id=299

Co-authored-by: Codex <noreply@openai.com>

program.go

@@ -1,11 +1,8 @@
 package process
 
 import (
-	"bytes"
 	"context"
 	"os/exec"
-	"strings"
-	"unicode"
 
 	core "dappco.re/go/core"
 	coreerr "dappco.re/go/log"
@@ -90,16 +87,30 @@ func (p *Program) RunDir(ctx context.Context, dir string, args ...string) (strin
 		return "", coreerr.E("Program.RunDir", "program name is empty", ErrProgramNameRequired)
 	}
 
-	var out bytes.Buffer
+	out := core.NewBuffer()
 	cmd := exec.CommandContext(ctx, binary, args...)
-	cmd.Stdout = &out
-	cmd.Stderr = &out
+	cmd.Stdout = out
+	cmd.Stderr = out
 	if dir != "" {
 		cmd.Dir = dir
 	}
 
 	if err := cmd.Run(); err != nil {
-		return strings.TrimRightFunc(out.String(), unicode.IsSpace), coreerr.E("Program.RunDir", core.Sprintf("%q: command failed", p.Name), err)
+		return trimRightSpace(out.String()), coreerr.E("Program.RunDir", core.Sprintf("%q: command failed", p.Name), err)
 	}
-	return strings.TrimRightFunc(out.String(), unicode.IsSpace), nil
+	return trimRightSpace(out.String()), nil
+}
+
+func trimRightSpace(s string) string {
+	trimFrom := len(s)
+	for i, r := range s {
+		if core.IsSpace(r) {
+			if trimFrom == len(s) {
+				trimFrom = i
+			}
+			continue
+		}
+		trimFrom = len(s)
+	}
+	return s[:trimFrom]
 }