Add runtime abstraction and agent loop

Co-authored-by: codegirl007 <codegirl-007@users.noreply.github.com>

agentbox/internal/agent/agent.go

@@ -0,0 +1,39 @@
+package agent
+
+import (
+	"context"
+	"time"
+
+	"agentbox/internal/environment"
+)
+
+type Observation struct {
+	Screenshot      []byte
+	Timestamp       time.Time
+	Logs            []environment.LogEntry
+	PreviousActions []environment.InputAction
+}
+
+type Step struct {
+	Number         int
+	Timestamp      time.Time
+	ScreenshotPath string
+	Message        string
+	Action         *environment.InputAction
+}
+
+type Decision struct {
+	Reason string
+	Action *environment.InputAction
+	Done   bool
+}
+
+type Agent interface {
+	Name() string
+	NextAction(
+		ctx context.Context,
+		task string,
+		history []Step,
+		observation Observation,
+	) (Decision, error)
+}