refactor(agent): improve code quality and restore summarization

Code review fixes:
- Use map for O(n) job lookup in cron service (was O(n²))
- Set DeleteAfterRun=true for one-time cron tasks
- Restore context compression/summarization to prevent context overflow
- Add pkg/utils/string.go with Unicode-aware Truncate function
- Simplify setupCronTool to return only CronService
- Change Chinese comments to English in context.go

Refactoring:
- Replace toolsSummary callback with SetToolsRegistry setter pattern
- This makes dependency injection clearer and easier to test

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/agent/context.go

@@ -11,13 +11,14 @@ import (
 	"github.com/sipeed/picoclaw/pkg/logger"
 	"github.com/sipeed/picoclaw/pkg/providers"
 	"github.com/sipeed/picoclaw/pkg/skills"
+	"github.com/sipeed/picoclaw/pkg/tools"
 )
 
 type ContextBuilder struct {
 	workspace    string
 	skillsLoader *skills.SkillsLoader
 	memory       *MemoryStore
-	toolsSummary func() []string // Function to get tool summaries dynamically
+	tools        *tools.ToolRegistry // Direct reference to tool registry
 }
 
 func getGlobalConfigDir() string {
@@ -28,9 +29,9 @@ func getGlobalConfigDir() string {
 	return filepath.Join(home, ".picoclaw")
 }
 
-func NewContextBuilder(workspace string, toolsSummaryFunc func() []string) *ContextBuilder {
-	// builtin skills: 当前项目的 skills 目录
-	// 使用当前工作目录下的 skills/ 目录
+func NewContextBuilder(workspace string) *ContextBuilder {
+	// builtin skills: skills directory in current project
+	// Use the skills/ directory under the current working directory
 	wd, _ := os.Getwd()
 	builtinSkillsDir := filepath.Join(wd, "skills")
 	globalSkillsDir := filepath.Join(getGlobalConfigDir(), "skills")
@@ -39,10 +40,14 @@ func NewContextBuilder(workspace string, toolsSummaryFunc func() []string) *Cont
 		workspace:    workspace,
 		skillsLoader: skills.NewSkillsLoader(workspace, globalSkillsDir, builtinSkillsDir),
 		memory:       NewMemoryStore(workspace),
-		toolsSummary: toolsSummaryFunc,
 	}
 }
 
+// SetToolsRegistry sets the tools registry for dynamic tool summary generation.
+func (cb *ContextBuilder) SetToolsRegistry(registry *tools.ToolRegistry) {
+	cb.tools = registry
+}
+
 func (cb *ContextBuilder) getIdentity() string {
 	now := time.Now().Format("2006-01-02 15:04 (Monday)")
 	workspacePath, _ := filepath.Abs(filepath.Join(cb.workspace))
@@ -80,11 +85,11 @@ Your workspace is at: %s
 }
 
 func (cb *ContextBuilder) buildToolsSection() string {
-	if cb.toolsSummary == nil {
+	if cb.tools == nil {
 		return ""
 	}
 
-	summaries := cb.toolsSummary()
+	summaries := cb.tools.GetSummaries()
 	if len(summaries) == 0 {
 		return ""
 	}