feat(billing): plan taxonomy reconciliation + Stripe sync + internal-tester allowlist (#164)

Co-authored-by: Michael Chihlas <michael@resolutionflow.com>
Co-committed-by: Michael Chihlas <michael@resolutionflow.com>

backend/tests/test_plans_public.py

@@ -14,7 +14,12 @@ from app.models.plan_limits import PlanLimits
 
 
 async def _seed_plan_limits(test_db, plan: str, max_users: int | None) -> None:
-    """Ensure a plan_limits row exists for the given plan name."""
+    """Ensure a plan_limits row exists with the given max_users.
+
+    Upserts: conftest seeds the canonical plans (free/starter/pro/enterprise)
+    so this helper has to overwrite max_users when a test wants different
+    values for fixture-driven assertions.
+    """
     existing = await test_db.get(PlanLimits, plan)
     if existing is None:
         test_db.add(
@@ -28,7 +33,9 @@ async def _seed_plan_limits(test_db, plan: str, max_users: int | None) -> None:
                 export_formats=["markdown", "text"],
             )
         )
-        await test_db.commit()
+    else:
+        existing.max_users = max_users
+    await test_db.commit()
 
 
 class TestGetPlansPublic: