re: 98.7% coverage, and the scale-free degeneracy fix is refuted

Under the winding gate, coverage is 6212/6294 (98.7%) with 82 misses left,
attributed 42 degenerate/extent, 31 winding, 9 coverage, 0 connectivity. The
biggest bucket turns out NOT to be the blocker: replacing the absolute area test
with a scale-free collinearity test decodes no more resources and raises
inconsistency 39 -> 44, and dropping the extent floor to 0.05 adds two. Both stay
as opt-in knobs (XBG7_REL_DEGEN, XBG7_MIN_EXTENT) rather than defaults. Also
fixed another stale 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(|_| "0.42 (default)".into())
+        std::env::var("XBG7_EDGE_CAP").unwrap_or_else(|_| "library default".into())
     );
 }