refactor(backend)!: separate algorithm and data layers

Reorganize algorithm packages by business responsibility, move orchestration into services, and keep database access behind pooled repositories.

Harden analysis API validation, remove unsafe legacy simulation endpoints, and add regression and architecture boundary coverage.

BREAKING CHANGE: legacy algorithm module paths and obsolete simulation endpoints are removed.

tests/api/test_sensor_placement_endpoints.py

@@ -55,7 +55,7 @@ def test_optimize_returns_analysis_run(monkeypatch):
     captured = {}
     monkeypatch.setattr(
         endpoint,
-        "pressure_sensor_placement_kmeans",
+        "optimize_sensor_placement_by_kmeans",
         lambda **kwargs: captured.update(kwargs) or {"run_id": RUN_ID},
     )
     monkeypatch.setattr(endpoint, "get_sensor_placement_run", lambda *_: _run())
@@ -74,7 +74,7 @@ def test_optimize_returns_analysis_run(monkeypatch):
 
     assert response.status_code == 200
     assert response.json()["run_id"] == str(RUN_ID)
-    assert captured["username"] == "alice"
+    assert captured["created_by"] == "alice"
 
 
 def test_optimize_rejects_project_mismatch(monkeypatch):