feat(viewer): data pack (.pak / IDXD) browser

Roadmap #3. The explorer can now open IPFB data packs — the game's ship/weapon/
mission definition tables. Selecting a `.pak` shows a master-detail browser:
entry list (hash · inner-format · identity) on the left, the selected IDXD
object's schema + explicit-field property table on the right.

Load path: a `.pak` selection reads the index plus its sibling `.pNN` segments
(ISO reader or extracted dir, probing p00.. until the first gap), assembles via
PakArchive::from_parts, and builds owned PakRow/PakDetail entirely off-thread —
so the UI holds only plain data (no borrow of a PakArchive, WASM-safe). Two
decode caps (64 MiB cumulative, 16 MiB/entry) keep a huge sound.pak from hanging;
over-budget entries show as "(not decoded)".

Wiring mirrors the texture path: new IsoLoaderMsg::PakLoaded → PendingPak staging
→ apply_pak. A shared reset (free GPU handle + clear texture/text/pak previews)
runs in both apply systems, so exactly one viewer is active per selection and the
prior GPU texture is always freed when switching modes.

Reuse over duplication: the CLI's inner_label / idxd_identity move into the
formats crate as pak::inner_format_label and IdxdObject::identity (bodies
verbatim → CLI output unchanged), now shared by CLI and GUI.

PakView registered unconditionally (wasm-safe; population native-only). ViewMode
unchanged — the central panel dispatches on the populated resource. Workspace
builds; 22 formats tests + all crate tests pass.

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

crates/sylpheed-formats/src/idxd.rs

@@ -171,6 +171,18 @@ impl IdxdObject {
         }
         out
     }
+
+    /// A short identity string for the object: the first of `ID` / `Name` /
+    /// `Model` present, else the schema hash. Shared by the CLI `pak list` and
+    /// the GUI pack browser.
+    pub fn identity(&self) -> String {
+        for key in ["ID", "Name", "Model"] {
+            if let Some(v) = self.get_raw(key) {
+                return format!("{key}={v}");
+            }
+        }
+        format!("schema {:08x}", self.schema_hash)
+    }
 }
 
 /// Extract the trailing string pool. Finds the smallest offset whose suffix is

crates/sylpheed-formats/src/pak.rs

@@ -262,6 +262,26 @@ fn be32(b: &[u8], o: usize) -> u32 {
     u32::from_be_bytes([b[o], b[o + 1], b[o + 2], b[o + 3]])
 }
 
+/// Best-effort human label for a decompressed entry's inner format, from its
+/// first bytes: `IDXD`, `xml`, a printable 4-char tag (RATC, IXUD, LSTA, …), or
+/// a hex fallback. Shared by the CLI `pak list` and the GUI pack browser.
+pub fn inner_format_label(payload: &[u8]) -> String {
+    if payload.len() < 4 {
+        return "empty".into();
+    }
+    let m = &payload[0..4];
+    if m == b"IDXD" {
+        "IDXD".into()
+    } else if payload.starts_with(b"<?xml") {
+        "xml".into()
+    } else if m.iter().all(|&b| b.is_ascii_graphic()) {
+        // Many inner formats are 4-char tags (RATC, T8aD, IXUD, LSTA, ttcf, …).
+        String::from_utf8_lossy(m).into_owned()
+    } else {
+        format!("{:02X}{:02X}{:02X}{:02X}", m[0], m[1], m[2], m[3])
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;