feat(freestyle): two-phase planning->execution driver (Slice 4)

- freestyle_planning.toml: analyst -> (approval) -> architect, producing
  execution_plan; analyst_freestyle.md surfaces open questions.
- TomlWorkflowLoader: requires_approval stage flag -> metadata.
- SessionOrchestrator: inline-prompt branch (metadata[promptInline]) +
  requestStageApproval helper reusing the existing pause/approve path.
- DefaultSessionOrchestrator: enterStage gates on requiresApproval
  (idempotent via resolved-approval lookup), preview derived from the
  gated stage's needs artifact; validatedArtifactContent accessor.
- FreestyleDriver: compiles validated plan, emits ExecutionPlanLockedEvent,
  runs phase 2 in-session via a runPhase2 seam; wired through ServerModule
  + Main (execution_plan kind registered).

examples/workflows/freestyle_planning.toml

@@ -0,0 +1,33 @@
+id = "freestyle_planning"
+start = "analyst"
+
+[[stages]]
+id = "analyst"
+prompt = "prompts/analyst_freestyle.md"
+produces = [{ name = "analysis", kind = "analysis" }]
+allowed_tools = ["file_read", "ShellTool"]
+token_budget = 16384
+max_retries = 2
+
+[[stages]]
+id = "architect"
+requires_approval = true
+prompt = "prompts/architect_freestyle.md"
+needs = ["analysis"]
+produces = [{ name = "execution_plan", kind = "execution_plan" }]
+token_budget = 16384
+max_retries = 2
+
+[[transitions]]
+id = "analyst-to-architect"
+from = "analyst"
+to = "architect"
+condition_type = "artifact_validated"
+condition_artifact_id = "analysis"
+
+[[transitions]]
+id = "architect-to-done"
+from = "architect"
+to = "done"
+condition_type = "artifact_validated"
+condition_artifact_id = "execution_plan"