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/llm_helper.go

@@ -0,0 +1,47 @@
+package activity
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/rockliang/poimen/workflows/activity/llm"
+	"github.com/rockliang/poimen/workflows/pkg/types"
+	"github.com/rockliang/poimen/workflows/prompts"
+)
+
+// CallRoleLLM is the shared pattern for calling an LLM with a role-based prompt.
+// Used by planner, implementer, and judge activities (DRY extraction).
+func CallRoleLLM(ctx context.Context, config types.OrchestratorConfig, role string, vars map[string]any) (string, error) {
+	client, err := llm.NewClient()
+	if err != nil {
+		return "", fmt.Errorf("failed to create LLM client: %w", err)
+	}
+
+	spec, exists := config.RolePrompts[role]
+	if !exists {
+		return "", fmt.Errorf("%s role prompt not configured", role)
+	}
+
+	// Render template
+	var content string
+	if spec.RawTemplate != "" {
+		content = spec.RawTemplate
+	} else {
+		content, err = prompts.Render(spec.TemplateRef, vars)
+		if err != nil {
+			return "", fmt.Errorf("failed to render %s template: %w", role, err)
+		}
+	}
+
+	// Call LLM
+	response, err := client.CreateMessage(ctx, llm.MessageInput{
+		Model:        spec.Model,
+		SystemPrompt: config.SystemPrompt,
+		Messages:     []llm.MessageParam{{Role: "user", Content: content}},
+	})
+	if err != nil {
+		return "", fmt.Errorf("%s LLM call failed: %w", role, err)
+	}
+
+	return response, nil
+}