fix(mesh): distinct assignment now covers grouped pools too

anchor_grouped_meshes takes the same taken set; a colliding grouped model is
re-placed whole past everything claimed, or keeps what it had. Runtime oracle
unchanged (45/46 exact, 0 unclaimed), coverage unchanged (6069), cross-container
inconsistency 62 -> 56, suite green.

It does not clear the n206 twin collapse: no alternative pool validates for the
loser, so that pair is a validator case (like eng_02_l before the cap move), not
a selection one. Also fixes a stale '0.28 (default)' label in edge_cap_sweep.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/sylpheed-formats/examples/edge_cap_sweep.rs

@@ -75,6 +75,6 @@ fn main() {
     }
     println!(
         "cap={}  models={models}  verts={verts}  shared={shared}  inconsistent={inconsistent}",
-        std::env::var("XBG7_EDGE_CAP").unwrap_or_else(|_| "0.28 (default)".into())
+        std::env::var("XBG7_EDGE_CAP").unwrap_or_else(|_| "0.42 (default)".into())
     );
 }