Initial commit: Cyrene Plugins SDK + Plugin Manager

Extracted from Cyrene main repo (backend/pkg/plugins + backend/plugin-manager).
Contains SDK interfaces (Plugin/Tool/HostAPI), 13 built-in plugins,
ToolRegistry with call log ring buffer, and Plugin Manager REST API service.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

sdk/base.go

@@ -0,0 +1,40 @@
+package sdk
+
+import (
+	"context"
+	"fmt"
+)
+
+// BasePlugin provides default implementations for optional Plugin methods.
+type BasePlugin struct{}
+
+func (BasePlugin) Init(_ context.Context, _ PluginConfig) error { return nil }
+
+func (BasePlugin) Start(_ context.Context, _ HostAPI) error { return nil }
+
+func (BasePlugin) Stop(_ context.Context) error { return nil }
+
+func (BasePlugin) Health(_ context.Context) error { return nil }
+
+// BaseTool provides a Validate default that checks required parameters.
+type BaseTool struct {
+	Def        ToolDefinition
+	Required   []string
+}
+
+func (b BaseTool) Definition() ToolDefinition { return b.Def }
+
+func (b BaseTool) Complexity() ToolComplexity { return ComplexitySimple }
+
+func (b BaseTool) Validate(args map[string]interface{}) error {
+	for _, key := range b.Required {
+		if _, ok := args[key]; !ok {
+			return fmt.Errorf("missing required parameter: %s", key)
+		}
+	}
+	return nil
+}
+
+func (b BaseTool) Execute(_ context.Context, _ map[string]interface{}) (*ToolResult, error) {
+	return nil, fmt.Errorf("not implemented")
+}