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/settings.go

@@ -0,0 +1,58 @@
+package sdk
+
+type SettingsAPI interface {
+	// Get reads the plugin's own config value (config_<name> table).
+	Get(key string) (interface{}, error)
+
+	// Set writes a config value to the plugin's own config table.
+	Set(key string, value interface{}) error
+
+	// List returns all keys matching the given prefix.
+	List(prefix string) ([]string, error)
+
+	// GetCore reads the core config table.
+	GetCore(key string) (interface{}, error)
+
+	// SetCore writes to the core config table.
+	SetCore(key string, value interface{}) error
+
+	// ListCore lists core config keys matching the prefix.
+	ListCore(prefix string) ([]string, error)
+
+	// GetPlugin reads another plugin's config table.
+	GetPlugin(plugin, key string) (interface{}, error)
+
+	// SetPlugin writes to another plugin's config table.
+	SetPlugin(plugin, key string, value interface{}) error
+
+	// ListPlugin lists another plugin's config keys matching the prefix.
+	ListPlugin(plugin, prefix string) ([]string, error)
+
+	// RegisterDef registers a config definition for UI display.
+	RegisterDef(def ConfigDef)
+
+	// Defs returns config definitions matching the prefix.
+	Defs(prefix string) []*ConfigDef
+
+	// Dump returns all config values.
+	Dump() map[string]interface{}
+
+	// Plugins returns a list of all plugin config namespaces.
+	Plugins() []string
+}
+
+// ConfigDef describes a configuration field for the WebUI.
+type ConfigDef struct {
+	Key         string      `json:"key"`
+	Default     interface{} `json:"default,omitempty"`
+	Type        string      `json:"type"`
+	DisplayName string      `json:"display_name"`
+	Description string      `json:"description,omitempty"`
+	Category    string      `json:"category,omitempty"`
+	Options     []string    `json:"options,omitempty"`
+	Min         float64     `json:"min,omitempty"`
+	Max         float64     `json:"max,omitempty"`
+	Step        float64     `json:"step,omitempty"`
+	Required    bool        `json:"required,omitempty"`
+	Secret      bool        `json:"secret,omitempty"`
+}