Implement adjudicated DO items across backend, frontend, deploy

From the ROADMAP adjudication (12 of 13 DO items; D2 is a commit action).

Backend:
- B3: pytest suite (auth, entity CRUD, rollup) + dev deps + pytest config
- B4: cap document uploads at TEN31_MAX_UPLOAD_SIZE (default 50MB), stream-
  checked with partial-file cleanup, 413 on overflow
- B7: type AuditLog.detail as dict|list|str|None to match the JSON column
- B10: index foreign-key columns (migration a7b8c9d0e1f2 + index=True)
- B11: cli delete-user logs file-removal errors instead of swallowing them

Frontend:
- F2: distinguish "server unreachable" from "logged out"; retry prompt
- F4: confirm before destructive holdings-replace on import; step progress
- F6: expandable audit-log detail with full JSON
- F7: empty-state on the Investments page
- F8: shared role helpers (WRITER_ROLES/canEditRound/isApprover), used by
  EntitiesList, AuditLog, Import, ValuationWorkflow

Deploy:
- D5: run tsc --noEmit before packaging (build script)
- D6: TEN31_LOG_LEVEL env var (defaults to info)

Verified: 8/8 backend tests pass; alembic upgrades to head with 13 FK
indexes; upload limit rejects oversized + cleans up; frontend tsc + vite
build clean; dev server serves and proxies to the API.

backend/tests/test_entities.py

@@ -0,0 +1,32 @@
+"""Entity CRUD round-trips through the API as a writer."""
+
+
+def test_entity_crud_roundtrip(auth_client):
+    # Create
+    created = auth_client.post(
+        "/api/entities",
+        json={"name": "Ten31 Fund I", "type": "fund", "vintage_year": 2025},
+    )
+    assert created.status_code == 201, created.text
+    entity_id = created.json()["id"]
+
+    # Read (single)
+    got = auth_client.get(f"/api/entities/{entity_id}")
+    assert got.status_code == 200
+    assert got.json()["name"] == "Ten31 Fund I"
+
+    # List
+    listed = auth_client.get("/api/entities")
+    assert listed.status_code == 200
+    assert any(e["id"] == entity_id for e in listed.json())
+
+    # Update
+    patched = auth_client.patch(
+        f"/api/entities/{entity_id}", json={"name": "Ten31 Fund I, LP"}
+    )
+    assert patched.status_code == 200
+    assert patched.json()["name"] == "Ten31 Fund I, LP"
+
+
+def test_get_missing_entity_404(auth_client):
+    assert auth_client.get("/api/entities/99999").status_code == 404