feat(formats,viewer): decode T8aD textures, RATC bundles, LSTA sprites

Add three static PAK-format decoders in the Bevy-free formats crate and
present them in the explorer:

- t8ad.rs: linear 32bpp A8R8G8B8 2D texture (UI/HUD art). Dims at
  0x14/0x18, header size keyed by the type field @0x1c (container-safe).
  Decodes the ~85% RGBA variants; defers the rest (likely DXT) rather
  than misdecoding.
- ratc.rs: nested resource bundle — lists named children by magic scan.
- lsta.rs: sprite list — walks the inline T8aD frames.

Viewer: PakContent gains T8ad/Lsta/Ratc, decoded off-thread and bounded
by an 8M-texel per-entry cap; detail views show the texture, a sprite
grid, and a child list with thumbnails. Decoded images carry a
"colours unverified" note — channel-order/sRGB stays on the dynamic-RE
backlog.

Tests: 12 new unit + 3 real-disc (T8aD >=70% decode over the hangar
pack, LSTA frames, RATC named children incl. a decodable T8aD).

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

crates/sylpheed-formats/src/lib.rs

@@ -31,6 +31,15 @@ pub mod ixud;
 // Embedded font (OTF / TTF / ttcf) metadata
 pub mod font;
 
+// T8aD 2D UI/HUD texture
+pub mod t8ad;
+
+// RATC nested resource bundle
+pub mod ratc;
+
+// LSTA sprite list (inline T8aD frames)
+pub mod lsta;
+
 // XISO reading is not available in-browser
 #[cfg(not(target_arch = "wasm32"))]
 pub mod xiso;
@@ -45,6 +54,8 @@ pub mod audio;
 pub use font::FontInfo;
 pub use idxd::{IdxdError, IdxdObject};
 pub use ixud::{Cue, Subtitle};
+pub use ratc::RatcChild;
+pub use t8ad::T8adImage;
 pub use pak::{PakArchive, PakEntry, PakError};
 pub use texture::{X360Texture, X360TextureFormat};
 pub use vfs::{GameAssets, VfsError};