ship: index-less brg/eng/sld parts never matched their GN frame — 34 ships assembled without a bridge

Tier 3 matched a part to its hardpoint by trailing index, so `e105_brg`
compared "01" == "" against GN_Bridge_01 and fell through silently. The runtime
capture is what exposed it: the game draws the bridge and places it at
[0, 70, -1850] rel e105_bdy_01, and assemble_ship emitted nothing there.

With no index to match on, take the lowest-numbered frame of the category.
Diffing assemble_ship part counts across every container: 34 (stage, ship)
entries gain parts — e102 +2 (bridge and engine), e104 +1, e105 +1, Stages
02-29. ship_audit is unchanged, so nothing regressed, and the capture now agrees
to dT 0.03 / dR 0.000.

Also fixes the diff itself: correlate_frames compared static against a rotation
sampled from the first block, which can belong to another INSTANCE of the class.
Scoped to the position-agreeing cluster, e105_eng_01 goes 1.711 -> 0.000 and
both e106 nacelles to 0.000. The one remaining rotation delta (e106_wep_02_01,
0.134) is a turret whose rotation varies by 0.182 between blocks that agree on
its position — the runtime disagrees with itself more than with the assembler.
The new rotVar column makes that distinction visible.

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

docs/re/BACKLOG.md

@@ -15,9 +15,12 @@ and to 0.000 in rotation for every part that does not move; see
 [`ship-placement-capture-generalisation.md`](ship-placement-capture-generalisation.md)
 §4. So look at **the viewer**: first that it passes `include_external = true`
 (`iso_loader.rs:4012` — with `false` an e106 loses its bridge and both nacelles,
-5 parts instead of 11), then its own transform stack. Two narrow format-side leftovers
-remain: `e105_brg` is never produced by `assemble_ship`, and `e105_eng_01`'s rotation
-differs by 1.711.
+5 parts instead of 11), then its own transform stack.
+
+One real format-side bug was found on the way and is **fixed**: index-less parts
+(`e105_brg`) never matched their `GN_Bridge_01` hardpoint, so 34 (stage, ship) entries
+— `e102`, `e104`, `e105` across Stages 02–29 — assembled without a bridge. The other
+apparent exception (`e105_eng_01` rotation) was an aggregation artefact and is 0.000.
 
 The original report and its reasoning follow.