mesh: strong relaxation morphs round the bad elements (harmonic interpolation within a reach)

The owner's direction: bad nodes move to better places, the nodes within a reach follow by
the graph Laplacian's harmonic extension, edges held, nothing outside the reach moves.
mesh.node.relax strong mode takes below and reach and reports each round.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

docs/mcp.md

@@ -210,11 +210,12 @@ When `mesh.quality` shows a handful of spikes in an otherwise good mesh:
    vertex nodes stay; nodes on a partition cut face move freely (both cells share them). The
    reply gives the nodes moved, the largest displacement, and the region's smallest scaled
    Jacobian, largest edge ratio and worst elements before and after. One undo step.
-   For a whole region at once, `mesh.node.relax {"mode": "strong", "bodies": ["Base"]}` (or
-   `"below": 0.7, "layers": 2` for the elements below 0.7 and two rings round them) optimises
-   every node together toward scaled Jacobian 1, edge and vertex nodes held, single elements
-   allowed to get worse on the way; it keeps the best state, never one with a lower smallest
-   scaled Jacobian, and replies the objective, min and mean per sweep (`history`).
+   For a whole region at once, `mesh.node.relax {"mode": "strong", "bodies": ["Base"], "below": 0.7}`
+   morphs the mesh round every element below 0.7: their nodes move to better places and the
+   nodes within `reach` (default three element lengths) follow by harmonic interpolation; edge
+   and vertex nodes are held, face nodes stay on their faces, nothing outside the reach moves,
+   and the smallest scaled Jacobian never drops. The reply lists each round's bad elements,
+   clusters and region size (`rounds`). It runs as a job (`job.status`, `job.cancel`).
 2. The relaxation is kept as a field of the model (`field`, default `Relax1`, …; saved with it).
    After a remesh, `mesh.node.relax.apply {"field": "Relax1"}` puts the relaxed shape on the new
    mesh (each node takes the displacement interpolated in the old cell it lies in, on its face,