viewer,ship: external parts ON by default + Ships catalog = composite ships only

Fixes the two things the user saw in the Ships browser:
- "Can't find the thrusters": show_external defaulted OFF, hiding the engine
  rig / bridge / turrets entirely. Externals are EXACT since the node-TRS fix,
  so the toggle now defaults ON (relabelled; off = bare hull bodies).
- "Some parts very far away": families without a composite scene graph (fighter
  morph sets like f002 whose detached parts are authored far from the origin,
  shared turret/prop part families) fell into the stack-at-origin fallback and
  rendered as piles with stray pieces. ShipModel now carries has_composite and
  the catalog lists only real assembled ships.

Offline audit across ALL stages (ship_audit example): the only far-away
outliers were composite-less f002 morph parts (now filtered); every capital
ship assembles coherently (e108 places its 7 turret instances, f105 its
mirrored shield generators). All primary composites are single-key tracks —
multikey exists only in animation composites (e901 attacks, missile-open),
which assemble_ship does not select.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/sylpheed-formats/examples/ship_audit.rs

@@ -0,0 +1,141 @@
+//! Audit static ship assembly across ALL stages: flag parts placed far outside
+//! their ship's cluster (placement bugs) and joint tracks with more than one
+//! keyframe (which the single-key TRS read does not model).
+//!   cargo run --release --example ship_audit -- <resource3d dir>
+use std::collections::HashSet;
+use sylpheed_formats::mesh::{xbg7_descriptor_range, xbg7_resource_names, Xbg7Model};
+use sylpheed_formats::ship::{assemble_ship, ships_in_container};
+
+fn be32(d: &[u8], o: usize) -> u32 {
+    if o + 4 > d.len() {
+        return 0;
+    }
+    u32::from_be_bytes([d[o], d[o + 1], d[o + 2], d[o + 3]])
+}
+
+/// Count joint-track records whose key count != 1 in a composite's descriptor.
+fn multikey_tracks(bytes: &[u8], comp: &str) -> usize {
+    let Some((desc, desc_end)) = xbg7_descriptor_range(bytes, comp) else { return 0 };
+    let d = &bytes[desc..desc_end];
+    let mut n = 0usize;
+    let mut i = 0usize;
+    while i + 4 <= d.len() {
+        let starts = &d[i..i.min(d.len() - 4) + 4] == b"rou_"
+            || (i + 3 <= d.len() && &d[i..i + 3] == b"GN_");
+        if !starts {
+            i += 1;
+            continue;
+        }
+        let mut j = i;
+        while j < d.len() && d[j] != 0 && d[j].is_ascii_graphic() {
+            j += 1;
+        }
+        let mut ff = i;
+        let scan_end = (i + 0x90).min(d.len().saturating_sub(4));
+        while ff < scan_end && be32(d, ff) != 0xFFFF_FFFF {
+            ff += 4;
+        }
+        if ff < scan_end && ff >= 0x10 {
+            let t44 = be32(d, ff - 0x10) as usize;
+            if t44 != 0 && t44 + 32 <= d.len() {
+                for k in 0..8 {
+                    let p = be32(d, t44 + k * 4) as usize;
+                    if p >= 0x50 && p + 16 <= d.len() {
+                        let head = be32(d, p - 0x50);
+                        if head != 1 && head != 0 {
+                            n += 1;
+                        }
+                    }
+                }
+            }
+        }
+        i = j.max(i + 1);
+    }
+    n
+}
+
+fn main() {
+    let dir = std::env::args().nth(1).unwrap();
+    let mut entries: Vec<_> = std::fs::read_dir(&dir)
+        .unwrap()
+        .filter_map(|e| e.ok())
+        .map(|e| e.path())
+        .filter(|p| {
+            let n = p.file_name().unwrap_or_default().to_string_lossy().to_string();
+            n.starts_with("Stage_") && n.ends_with(".xpr")
+        })
+        .collect();
+    entries.sort();
+
+    for path in entries {
+        let stage = path.file_name().unwrap().to_string_lossy().to_string();
+        let bytes = std::fs::read(&path).unwrap();
+        let names = xbg7_resource_names(&bytes);
+
+        // Multi-key animation tracks per composite (breaks the single-key read).
+        for n in names.iter().filter(|n| n.contains("rou_") && !n.contains("break")) {
+            let mk = multikey_tracks(&bytes, n);
+            if mk > 0 {
+                println!("MULTIKEY {stage} {n}: {mk} tracks");
+            }
+        }
+
+        for ship in ships_in_container(&bytes) {
+            if ship.parts.len() < 2 {
+                continue;
+            }
+            let placed = assemble_ship(&bytes, &ship.id, true);
+            if placed.len() < 2 {
+                continue;
+            }
+            let want: HashSet<String> = placed.iter().map(|p| p.resource.clone()).collect();
+            let models = Xbg7Model::models_named(&bytes, &want, &|| false);
+            // Per-placement world centroid.
+            let mut cents: Vec<(String, [f32; 3])> = Vec::new();
+            for p in &placed {
+                let Some(m) = models.iter().find(|m| m.name == p.resource) else { continue };
+                let (mut c, mut n) = ([0.0f32; 3], 0f32);
+                for sub in &m.meshes {
+                    for v in &sub.positions {
+                        let w = p.apply(*v);
+                        c[0] += w[0];
+                        c[1] += w[1];
+                        c[2] += w[2];
+                        n += 1.0;
+                    }
+                }
+                if n > 0.0 {
+                    cents.push((p.resource.clone(), [c[0] / n, c[1] / n, c[2] / n]));
+                }
+            }
+            if cents.len() < 2 {
+                continue;
+            }
+            // Ship cluster = median centroid; flag parts > 3× the median spread.
+            let med = |k: usize| -> f32 {
+                let mut v: Vec<f32> = cents.iter().map(|(_, c)| c[k]).collect();
+                v.sort_by(|a, b| a.partial_cmp(b).unwrap());
+                v[v.len() / 2]
+            };
+            let m = [med(0), med(1), med(2)];
+            let dists: Vec<f32> = cents
+                .iter()
+                .map(|(_, c)| {
+                    ((c[0] - m[0]).powi(2) + (c[1] - m[1]).powi(2) + (c[2] - m[2]).powi(2)).sqrt()
+                })
+                .collect();
+            let mut sd: Vec<f32> = dists.clone();
+            sd.sort_by(|a, b| a.partial_cmp(b).unwrap());
+            let spread = sd[sd.len() / 2].max(50.0);
+            for ((res, c), dist) in cents.iter().zip(&dists) {
+                if *dist > 6.0 * spread && *dist > 800.0 {
+                    println!(
+                        "OUTLIER {stage} {}: {res} centroid=[{:.0} {:.0} {:.0}] dist={:.0} (spread {:.0})",
+                        ship.id, c[0], c[1], c[2], dist, spread
+                    );
+                }
+            }
+        }
+    }
+    println!("audit done");
+}