refactor: pluginize text cleaning and tool NoMemory control

- SDK: ToolDef.NoMemory field, PluginSDK.RegisterTextCleaner/TextCleaners
- Registry: aggregate text cleaners from plugins, expose CleanText()
- Memory: replace hardcoded QQ regex CleanTemplateText with dynamic CleanText/SetTextCleaner
- StageHost: add ToolDef(name) lookup
- eventloop: check ToolDef.NoMemory before emitMemoryCandidate
- context/Prune: replace hardcoded agentcli/terminal source filter with ToolsUsed NoMemory check
- agentcli/cmd: mark tools with NoMemory: true
- main.go: wire memory.SetTextCleaner(pluginReg.CleanText)

internal/memory/cut_test.go

@@ -101,7 +101,7 @@ func TestCutExactRemoveTimestamp(t *testing.T) {
 	got := CutExact("[15:04] 今天天气不错")
 	for _, g := range got {
 		if g == "15" || g == "04" || g == "15:04" {
-			t.Errorf("timestamp should be removed by CleanTemplateText, got %q in %v", g, got)
+			t.Errorf("timestamp should be removed by CleanText, got %q in %v", g, got)
 		}
 	}
 }