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)

_sdk_local/sdk/knowledge.go

@@ -0,0 +1,14 @@
+package sdk
+
+// KnowledgeAPI provides access to the knowledge store.
+type KnowledgeAPI interface {
+	Search(query string, topK int) ([]*Knowledge, error)
+	Add(name, content string) error
+	List() ([]string, error)
+}
+
+// Knowledge represents a knowledge entry.
+type Knowledge struct {
+	Name    string `json:"name"`
+	Content string `json:"content"`
+}