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/example/files/plg.json

@@ -0,0 +1,11 @@
+{
+  "name": "files",
+  "name_zh": "文件系统",
+  "name_en": "File System",
+  "version": "1.0.0",
+  "description": "文件系统操作工具集（读取/写入/编辑/列表），提供沙箱化文件访问，支持配置工作目录。",
+  "author": "HomeAgent",
+  "entry": "plugin.so",
+  "tags": ["files", "filesystem"],
+  "targets": "linux/amd64"
+}