feat(formats,cli): decode XBG7 stage containers + fix weapon layout

Stage containers (hidden/resource3d/Stage_S*.xpr) are collections of up to
~450 enemy/prop sub-models, not single meshes. Xbg7Model::stage_models decodes
them: each resource is a [12-byte header][index buffer][vertex buffer] block
(index count = descriptor marker, vertex count = u32 32 bytes before it) whose
on-disc offset is NOT stored, so it is located by content — one O(file) pass per
stride finds vertex-buffer starts (unit NORMAL at +12 whose previous slot isn't)
and each resource is pinned to the candidate whose indices validate and produce
non-degenerate, well-connected triangles. A connectivity gate (mean triangle
edge <= 0.28x the bbox diagonal) rejects spiky mis-anchors. ~4993 sub-models
decode across the 22 stages.

The same insight fixes the weapon single-model layout: it is [12-byte header]
[index][vertex] too, not [index][12-byte gap][vertex]. Reading indices from the
block start turned the 12 header bytes into 6 junk indices (2 leading degenerate
triangles — the recurring stray-triangle artifact) and dropped the last 6 real
indices. Skipping the header leaves vertex offsets identical (coverage unchanged
at 36/166) and corrects the triangle list. Verified on wep_00/03/04.

Adds `sylpheed-cli mesh {info,render}` — a headless software rasterizer that
writes a shaded PNG (orthographic, z-buffered, two-sided), so recovered geometry
can be verified without the GUI. Stages render as a normalised thumbnail grid;
--only filters sub-models.

Tests: stage_models_{decode,sweep,quality_audit}; docs/re updated (xbg7-mesh.md
evidence log + INDEX.md).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/sylpheed-formats/tests/mesh_disc.rs

@@ -121,3 +121,114 @@ fn complex_body_mesh_is_declined_not_garbage() {
         }
     }
 }
+
+/// Stage containers decode multiple enemy/prop sub-models via content anchoring.
+/// Prints coverage; asserts the known-good Stage_S10 meshes decode with sane geometry.
+#[test]
+#[ignore]
+fn stage_models_decode() {
+    use sylpheed_formats::mesh::Xbg7Model;
+    let dir = std::env::var("SYLPHEED_RES3D").unwrap_or_else(|_| {
+        "/home/fabi/RE Project Sylpheed/sylph_extract/hidden/resource3d".to_string()
+    });
+    let path = format!("{dir}/Stage_S10.xpr");
+    let bytes = std::fs::read(&path).expect("read Stage_S10");
+    let models = Xbg7Model::stage_models(&bytes);
+    for m in &models {
+        let (v, t) = m.totals();
+        let mut lo = [f32::MAX; 3];
+        let mut hi = [f32::MIN; 3];
+        for sub in &m.meshes {
+            for p in &sub.positions {
+                for a in 0..3 {
+                    lo[a] = lo[a].min(p[a]);
+                    hi[a] = hi[a].max(p[a]);
+                }
+            }
+        }
+        let ext = [hi[0] - lo[0], hi[1] - lo[1], hi[2] - lo[2]];
+        println!(
+            "  {:16} v={v} t={t} bbox=[{:.1},{:.1},{:.1}]",
+            m.name, ext[0], ext[1], ext[2]
+        );
+    }
+    // Known: e003 (main enemy, ~1400 tris) must be among the decoded models.
+    let e003 = models.iter().find(|m| m.name == "e003").expect("e003 decoded");
+    let (v, t) = e003.totals();
+    assert_eq!(v, 2383, "e003 vertex count");
+    assert!(t > 1400, "e003 triangle count {t}");
+    assert!(models.len() >= 3, "at least 3 stage sub-models, got {}", models.len());
+}
+
+/// Timing/coverage sweep across all stage containers (manual; release recommended).
+#[test]
+#[ignore]
+fn stage_models_sweep() {
+    use sylpheed_formats::mesh::Xbg7Model;
+    use std::time::Instant;
+    let dir = std::env::var("SYLPHEED_RES3D").unwrap_or_else(|_| {
+        "/home/fabi/RE Project Sylpheed/sylph_extract/hidden/resource3d".to_string()
+    });
+    let mut names: Vec<_> = std::fs::read_dir(&dir)
+        .unwrap()
+        .filter_map(|e| e.ok().map(|e| e.file_name().into_string().unwrap()))
+        .filter(|n| n.starts_with("Stage_") && n.ends_with(".xpr"))
+        .collect();
+    names.sort();
+    let mut tot = 0usize;
+    for n in &names {
+        let bytes = std::fs::read(format!("{dir}/{n}")).unwrap();
+        let t0 = Instant::now();
+        let models = Xbg7Model::stage_models(&bytes);
+        let dt = t0.elapsed().as_millis();
+        tot += models.len();
+        println!("{n:16} {:>4} MB  {:>3} models  {:>5} ms", bytes.len()/1_000_000, models.len(), dt);
+    }
+    println!("TOTAL stage sub-models decoded: {tot}");
+}
+
+/// Quality audit: for a big stage, verify decoded models are real geometry
+/// (bounded bbox, low full-mesh degeneracy) rather than false anchors.
+#[test]
+#[ignore]
+fn stage_models_quality_audit() {
+    use sylpheed_formats::mesh::Xbg7Model;
+    let dir = std::env::var("SYLPHEED_RES3D").unwrap_or_else(|_| {
+        "/home/fabi/RE Project Sylpheed/sylph_extract/hidden/resource3d".to_string()
+    });
+    let bytes = std::fs::read(format!("{dir}/Stage_S07.xpr")).unwrap();
+    let models = Xbg7Model::stage_models(&bytes);
+    let (mut small, mut mid, mut huge, mut dupnames) = (0, 0, 0, 0);
+    let mut seen = std::collections::HashSet::new();
+    let mut worst_deg = 0.0f32;
+    for m in &models {
+        if !seen.insert(m.name.clone()) { dupnames += 1; }
+        let mut lo = [f32::MAX; 3]; let mut hi = [f32::MIN; 3];
+        let mut deg = 0usize; let mut tot = 0usize;
+        for sub in &m.meshes {
+            for p in &sub.positions { for a in 0..3 { lo[a]=lo[a].min(p[a]); hi[a]=hi[a].max(p[a]); } }
+            for tri in sub.indices.chunks_exact(3) {
+                let (a,b,c)=(tri[0] as usize,tri[1] as usize,tri[2] as usize);
+                if a>=sub.positions.len()||b>=sub.positions.len()||c>=sub.positions.len(){continue;}
+                let pa=sub.positions[a]; let pb=sub.positions[b]; let pc=sub.positions[c];
+                let u=[pb[0]-pa[0],pb[1]-pa[1],pb[2]-pa[2]];
+                let v=[pc[0]-pa[0],pc[1]-pa[1],pc[2]-pa[2]];
+                let cx=[u[1]*v[2]-u[2]*v[1],u[2]*v[0]-u[0]*v[2],u[0]*v[1]-u[1]*v[0]];
+                if 0.5*(cx[0]*cx[0]+cx[1]*cx[1]+cx[2]*cx[2]).sqrt()<1e-9 { deg+=1; }
+                tot+=1;
+            }
+        }
+        let ext = (hi[0]-lo[0]).max(hi[1]-lo[1]).max(hi[2]-lo[2]);
+        let df = if tot>0 { deg as f32/tot as f32 } else {1.0};
+        worst_deg = worst_deg.max(df);
+        if ext < 200.0 { small += 1; } else if ext < 5000.0 { mid += 1; } else { huge += 1; }
+    }
+    println!("S07: {} models | small(<200u)={} mid={} huge(>5k)={} | dup-names={} | worst full-mesh degeneracy={:.1}%",
+        models.len(), small, mid, huge, dupnames, worst_deg*100.0);
+    // Each XBG7 resource must anchor to a *distinct* block (no collisions), the
+    // bulk must be bounded-scale geometry, and none may be mostly-degenerate.
+    assert_eq!(dupnames, 0, "no two resources should anchor to the same block");
+    assert!(small + mid > models.len() * 9 / 10, "≥90% bounded-scale geometry");
+    assert!(huge < models.len() / 20, "few huge (skybox-plane) models");
+    assert!(worst_deg < 0.35, "no model should be mostly-degenerate");
+}