feat(harness): workflow.yaml as single source of truth + workflow.py loader (F2)

- workflow.yaml: 8-phase definition, data-driven prerequisites, no hardcoded ladder
- workflow.py: load_workflow() reader; max_phase=len(phases), decision_min_phase
  derived from prerequisites scan (no duplication)
- 6 tests: phase count, decision_min_phase derivation, name lookup (incl. F8
  presence -- the JS drift bug structurally impossible now), artifacts_out,
  advance strategy, schema_version. All 8 harness tests pass.

harness/workflow.yaml

@@ -0,0 +1,59 @@
+# harness/workflow.yaml — single source of workflow truth (spec F2, §5.3)
+# phase.py, il gate e la skill leggono tutti da qui. Nessuna costante duplicata.
+# Editare questo file per cambiare il workflow (aggiungere/riordinare/fondere/skip fasi).
+
+schema_version: 1
+
+phases:
+  - id: F1
+    name: chiarimento
+    advance: kind:phase
+    prerequisites: []
+    artifacts_out: []
+  - id: F2
+    name: memoria
+    advance: auto_if_empty
+    prerequisites: []
+    artifacts_out: []
+  - id: F3
+    name: riscrittura
+    advance: kind:phase
+    prerequisites:
+      - decision_exists: question_rewritten
+    artifacts_out: [question.md]
+  - id: F4
+    name: schema_linking
+    advance: reviewer_decide
+    prerequisites: []
+    artifacts_out: [schema_linking.json]
+  - id: F5
+    name: sintesi
+    advance: kind:phase
+    prerequisites:
+      - file_validates: [schema_linking.json, SchemaLinking]
+    artifacts_out: []
+  - id: F6
+    name: cte
+    advance: auto_if_empty_or_skipped
+    prerequisites:
+      - any:
+          - decision_subject_exists: [phase_skipped, "phase:6"]
+          - all_ctes_approved: true
+    artifacts_out: [cte_plan.json, ctes/, cte_tests.json]
+  - id: F7
+    name: sql_finale
+    advance: kind:phase
+    prerequisites:
+      - decision_exists: sql_approved
+    artifacts_out: [sql_final.sql]
+  - id: F8
+    name: datamart
+    advance: reviewer_decide
+    prerequisites:
+      - any:
+          - decision_exists: datamart_requested
+          - decision_exists: datamart_declined
+    artifacts_out: []
+
+decision_min_phase: auto
+max_phase: auto