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/planner.go

@@ -0,0 +1,47 @@
+package activity
+
+import (
+	"context"
+
+	"github.com/rockliang/poimen/workflows/pkg/types"
+)
+
+type PlanningInput struct {
+	Config      types.OrchestratorConfig
+	BoardState  string
+	RepoPath    string
+	Milestone   string
+	TaskResults []types.TaskUnitOutput
+}
+
+type TaskDispatch struct {
+	TaskID      string
+	PromptSpec  types.PromptSpec
+	BaseTimeout *int64
+}
+
+type PlanningOutput struct {
+	TasksToDispatch      []string
+	CompletedBranches    []string
+	SubmilestoneComplete bool
+}
+
+func PlanningActivity(ctx context.Context, in PlanningInput) (PlanningOutput, error) {
+	response, err := CallRoleLLM(ctx, in.Config, "planner", map[string]any{
+		"SystemPrompt": in.Config.SystemPrompt,
+		"BoardState":   in.BoardState,
+		"Milestone":    in.Milestone,
+		"Config":       in.Config,
+	})
+	if err != nil {
+		return PlanningOutput{}, err
+	}
+
+	// TODO: parse LLM response into task dispatch list
+	_ = response
+	return PlanningOutput{
+		TasksToDispatch:      []string{},
+		CompletedBranches:    []string{},
+		SubmilestoneComplete: false,
+	}, nil
+}