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/types.go

@@ -0,0 +1,21 @@
+package activity
+
+import "github.com/rockliang/poimen/workflows/pkg/types"
+
+// Re-export from pkg/types for convenience within activity package.
+type ModelSpec = types.ModelSpec
+type PromptSpec = types.PromptSpec
+type SkillRef = types.SkillRef
+type OrchestratorConfig = types.OrchestratorConfig
+type TaskUnitOutput = types.TaskUnitOutput
+type EdgeWithWording = types.EdgeWithWording
+type RelationWording = types.RelationWording
+type CanvasWithRelationsData = types.CanvasWithRelationsData
+type FetchCanvasRelationsInput = types.FetchCanvasRelationsInput
+type CanvasReasonerInput = types.CanvasReasonerInput
+type GraphRAGQueryInput = types.GraphRAGQueryInput
+type GraphRAGQueryOutput = types.GraphRAGQueryOutput
+type QueryPathData = types.QueryPathData
+type CanvasCompatibilityInput = types.CanvasCompatibilityInput
+type IndexGraphRAGInput = types.IndexGraphRAGInput
+type IndexGraphRAGOutput = types.IndexGraphRAGOutput