Naming/contract delta: _root_cfg, _device_boundaries, blocked_coarse_tables; NODE vs EDGE frame

- Coarse/fine name the two members of any pair (Hierarchy docstring); only the
  misleading blocked_base_tables -> blocked_coarse_tables. prepare_fine_boundary
  and blocked_fine_tables keep their pair-relative names.
- Depth-1 static circles use the integer-NODE frame (unchanged behavior); the
  root EDGE frame applies to refined levels only. Contract text corrected.
- _kernel_configs documents why it stays distinct from Hierarchy.configs.
- Drop the stale re-export comment; two tests import table builders from
  refinement_tables. Mechanical caller renames for this delta only.
No numerical code or config derivation changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/validation/multigrid/test_refinement_blocked_fine.py

@@ -21,7 +21,8 @@ from CelerisLab.lbm.descriptors import D2Q9_EX, D2Q9_EY
 from CelerisLab.lbm.descriptors import SOLID
 from CelerisLab.lbm.refinement import (ACTIVE, INNER_GHOST, OUTER_GHOST, FixedPatch2D,
                                        prepare_fine_boundary)
-from CelerisLab.lbm.refinement_stepper import FixedPatchStepper, blocked_fine_tables
+from CelerisLab.lbm.refinement_stepper import FixedPatchStepper
+from CelerisLab.lbm.refinement_tables import blocked_fine_tables
 
 NX, NY, BOUNDS, STEPS = 32, 24, (8, 6, 24, 18), 8
 FINE_BLOCKS = ((32, 40), (16, 20), (16, 10))  # fine window 32x40: 1x1, 2x2, 4x2
@@ -186,8 +187,8 @@ class BlockedFineCPU(unittest.TestCase):
             backend, calls = self.mocked_backend([circle(spec)])
             c, f = backend._levels
             coarse, cur, spare = c.current, f.current, f.spare
-            flags, kind = backend._level_boundaries[1].flags, backend._levels[1].kind
-            velocity = backend._level_boundaries[1].device.get("surface_velocity")
+            flags, kind = backend._device_boundaries[1].flags, backend._levels[1].kind
+            velocity = backend._device_boundaries[1].device.get("surface_velocity")
             self.assertEqual(velocity is None, spec is None)
             backend.step(1)
             backend.close()
@@ -213,7 +214,7 @@ class BlockedFineCPU(unittest.TestCase):
         for speed in (0.0, .002):  # any spec, even zero amplitude
             backend, calls = self.mocked_backend([circle(actuation(speed))])
             self.assertIsNotNone(backend._fine_tables["surface_velocity"])
-            del backend._level_boundaries[1].device["surface_velocity"]
+            del backend._device_boundaries[1].device["surface_velocity"]
             with self.assertRaisesRegex(RuntimeError, "Surface velocity device buffer is missing"):
                 backend.step(1)
             names = [name for name, _ in calls]