revert(mesh): withdraw the neighbourhood anchor -- it regressed the e106 twin mirror

The neighbourhood anchor (f18d591) and its refinement (27a0701) took
cross-container inconsistency from 125 to 51 with coverage unchanged, and made
e106 render as a destroyer rather than a slab. Both are reverted.

ship::tests::static_assembly_matches_runtime_capture is gated on SYLPHEED_ISO, so
it SKIPS in an ordinary cargo test -- which is why the regression was invisible
in every suite run so far. With the ISO it fails:

  e106_bdy_01: static M row0 [-1.0, 0.0, 0.0] != captured [1.0, 0.0, 0.0]

e106_bdy_01 and _02 are a mirrored pair whose two buffers hold the same geometry
reflected in X, and BOTH resources currently decode to the SAME buffer (identical
counts, span and mean_x). apply_twin_mirrors picks which instance to reflect from
the sign of that mean_x, so which buffer wins flips the decision:

  before  both twins mean_x = -66.83  -> mirror bdy_02  (matches the capture)
  after   both twins mean_x = +66.83  -> mirror bdy_01  (contradicts it)

Neither is right -- two resources sharing one decode is itself the bug and the
mirror heuristic has been compensating. The capture is ground truth, so a change
that contradicts it does not ship. The real fix must give each twin its own
buffer first.

Kept from the attempt: this test now also asserts the SET of static placements
against the capture (allow-list {e303_wep_01} for vbase dedup), so extra
placements can finally fail it -- the direction it could never fail in before.

Docs, backlog, INDEX and the ignored test's message all corrected to say
diagnosed-not-fixed rather than fixed.

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

crates/sylpheed-formats/src/ship.rs

@@ -615,6 +615,27 @@ mod tests {
                 }
             }
         }
+        // ── Extras: the direction this test could not previously fail in. ──
+        // The loop above walks the CAPTURE's parts and looks each up in ours, so
+        // a static placement with no counterpart was invisible to it — which is
+        // how a resource decoded 100x too large (`e303_wep_01`, 2026-08-12) sat
+        // here unnoticed. Pin the set instead: the capture legitimately misses
+        // repeated instances of a shared resource (vbase dedup), so `e303_wep_01`
+        // is expected; anything else appearing only in the static assembly is a
+        // regression.
+        let captured: std::collections::BTreeSet<&str> =
+            cap.parts.iter().map(|p| p.part.as_str()).collect();
+        let extra: std::collections::BTreeSet<&str> = placed
+            .iter()
+            .map(|p| p.resource.as_str())
+            .filter(|r| !captured.contains(r))
+            .collect();
+        let allowed: std::collections::BTreeSet<&str> = ["e303_wep_01"].into_iter().collect();
+        assert_eq!(
+            extra, allowed,
+            "static placements with no counterpart in the runtime capture"
+        );
+
         // Multi-instance coverage the capture couldn't see (vbase dedup).
         let count = |res: &str| placed.iter().filter(|p| p.resource == res).count();
         assert_eq!(count("e106_eng_01"), 2, "both engine nacelles placed");