feat(formats): recover IPFB TOC name-hash; look up entries by path

The pak TOC key was previously an unknown hash (crc32/fnv/djb2/… ruled
out), forcing content-only lookup. Recovered it by static RE of the
retail title:

  sub_824609C8 (pak lookup-by-name) dups the requested path, lowercases
  it (sub_825F4F90), hashes with sub_82455C78, then binary-searches the
  sorted TOC. sub_82455C78 is a per-byte Barrett-reduced polynomial hash
  (modulus 0x00FFF9D7, reciprocal 0x80031493): the low 24 bits are the
  modular hash, the top byte an 8-bit additive checksum of the bytes.

New `hash` module reproduces it exactly (faithful op sequence, no
textbook %). Verified against the real disc: name_hash("files.tbl") ==
0x83421153 and name_hash("eng\\weapon.tbl") == 0x900C8DCD, both present
in retail TOCs. Add PakArchive::find_by_name / read_by_name and a disc
integration test resolving eng\weapon.tbl by path (→ valid IDXD).

Note: retail paths use backslash separators (eng\weapon.tbl).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/sylpheed-formats/src/lib.rs

@@ -16,6 +16,9 @@
 pub mod texture;
 pub mod vfs;
 
+// IPFB TOC name-hash (path → 32-bit key), recovered from the retail title
+pub mod hash;
+
 // IPFB archive (`*.pak` index + `*.pNN` segments) reader
 pub mod pak;