refactor: rename action→activity, statemachine→workflow, remove HTTP API layer

- action/ → activity/ (Temporal activities)
- statemachine/ → workflow/ (Temporal workflows)
- Removed internal/api/ and cmd/server/ (api-gw handles HTTP, Temporal is the API)
- Created pkg/types/types.go as single source of truth for all shared types
- Extracted CallRoleLLM helper (DRY: implementer/planner/judge shared pattern)
- Fixed circular import: workflow_graph_query uses string activity names
- Fixed logger.logf → logger.Info/Warn (method didn't exist)
- Fixed routing types: added Branches, Activity, BackoffSeconds, TaskActivity
- Fixed db.Canvas.Name, db.Client→DB, GetWorkflow→FetchWorkflow
- Removed unused imports
- All tests pass, build clean, vet clean

activity/fetch_canvas_relations.go

@@ -0,0 +1,80 @@
+package activity
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/rockliang/poimen/workflows/pkg/db"
+)
+
+// FetchCanvasRelationsActivity fetches canvas + relations from DB
+func FetchCanvasRelationsActivity(ctx context.Context, input FetchCanvasRelationsInput) (CanvasWithRelationsData, error) {
+	logger := newActivityLogger(ctx)
+	output := CanvasWithRelationsData{
+		WorkflowID: input.WorkflowID,
+		Version:    input.Version,
+		Nodes:      []db.WorkflowNode{},
+		Edges:      []db.WorkflowEdge{},
+		Relations:  []EdgeWithWording{},
+	}
+
+	logger.Info("Fetching canvas relations: %s v%d", input.WorkflowID, input.Version)
+
+	// Get database client from context or activity manager
+	dbClient, ok := ctx.Value("db_client").(*db.DB)
+	if !ok {
+		return output, fmt.Errorf("database client not in context")
+	}
+
+	// Fetch workflow
+	workflow, err := dbClient.FetchWorkflow(ctx, input.WorkflowID, "")
+	if err != nil {
+		return output, fmt.Errorf("failed to get workflow: %w", err)
+	}
+
+	// Parse canvas nodes and edges
+	var nodes []db.WorkflowNode
+	if err := json.Unmarshal([]byte(workflow.Nodes), &nodes); err != nil {
+		return output, fmt.Errorf("failed to parse nodes: %w", err)
+	}
+
+	var edges []db.WorkflowEdge
+	if err := json.Unmarshal([]byte(workflow.Edges), &edges); err != nil {
+		return output, fmt.Errorf("failed to parse edges: %w", err)
+	}
+
+	output.Nodes = nodes
+	output.Edges = edges
+	output.UpdatedAt = workflow.UpdatedAt.String()
+
+	// Fetch workflow relations
+	relations, err := dbClient.GetWorkflowRelations(ctx, input.WorkflowID, input.Version)
+	if err != nil {
+		// Relations may not exist for old canvases - this is OK
+		logger.Warn("Failed to fetch relations: %v", err)
+		return output, nil
+	}
+
+	// Map to EdgeWithWording
+	for _, rel := range relations {
+		edge := EdgeWithWording{
+			ID:             rel.ID,
+			Source:         rel.SourceNodeID,
+			Target:         rel.TargetNodeID,
+			RelationType:   rel.RelationType,
+			RelationLabel:  rel.Label,
+			CreatedAt:      rel.CreatedAt.String(),
+		}
+
+		// Parse relation wording JSON
+		if err := json.Unmarshal(rel.RelationWording, &edge.RelationWording); err != nil {
+			logger.Warn("Failed to parse relation wording: %v", err)
+		}
+
+		output.Relations = append(output.Relations, edge)
+	}
+
+	logger.Info("Fetched %d nodes, %d edges, %d relations", len(output.Nodes), len(output.Edges), len(output.Relations))
+	return output, nil
+}