Initial crate: all 16 single-byte MS-DOS code pages, bidirectional

Tables are generated from the Unicode Consortium's Microsoft mappings
(VENDORS/MICSFT/PC), vendored in data/ and regenerated by
tools/gen_tables.py. Decode is fallible because 857/864/869/874 leave
byte values undefined; decode_lossy substitutes U+FFFD. Every table is
a verified bijection, so defined bytes round-trip exactly.

README.md

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+# msdos-encodings
+
+Bidirectional, emulator-grade conversion between MS-DOS code pages and Unicode —
+without linking ICU. The crate owns the canonical Microsoft tables, so it stays
+small, self-contained, and cross-compiles cleanly.
+
+These are strictly **Microsoft's** mappings as published by the Unicode
+Consortium (`VENDORS/MICSFT/PC/`) — not the IBM or Oracle variants, which
+differ in a handful of slots.
+
+```rust
+use msdos_encodings::DosEncoding;
+
+let enc = DosEncoding::default(); // code page 437
+assert_eq!(enc.decode(b"Caf\x82").unwrap(), "Café");
+assert_eq!(enc.encode("Café").unwrap(), b"Caf\x82");
+
+// Pick by numeric code page (e.g. from CHCP or locale data):
+let enc = DosEncoding::from_code_page(866).unwrap();
+assert_eq!(enc.decode(&[0x80]).unwrap(), "А"); // DOS Cyrillic Russian
+
+// Four pages leave bytes undefined; decode is fallible, or go lossy:
+assert!(DosEncoding::Cp874.decode(&[0xFF]).is_err());
+assert_eq!(DosEncoding::Cp874.decode_lossy(&[0xFF]), "\u{FFFD}");
+```
+
+## Status
+
+- **All sixteen single-byte DOS pages** — implemented, decode + encode:
+  437, 737, 775, 850, 852, 855, 857, 860, 861, 862, 863, 864, 865, 866, 869, 874.
+- **Double-byte CJK pages** (932 Shift-JIS, 936 GBK, 949 Korean, 950 Big5) —
+  planned, to be codegen'd the same way and feature-gated.
+
+## Fidelity notes
+
+- Every table is a verified bijection: anything a page decodes re-encodes to
+  the identical bytes.
+- Code pages 857, 864, 869, and 874 leave some byte values undefined, so
+  `decode` returns a `Result`; `decode_lossy` substitutes U+FFFD.
+- Microsoft's CP864 (DOS Arabic) maps `0x25` to ARABIC PERCENT SIGN — the low
+  half is *not* pure ASCII, and `%` itself is unmappable. This is faithful to
+  the source table.
+
+## Regenerating tables
+
+`src/tables.rs` is generated from the vendored mapping files in `data/`
+(needs Python ≥ 3.10 and `rustfmt` on `PATH`):
+
+```sh
+uv run tools/gen_tables.py
+```
+
+## Scope
+
+Text-encoding conversion only. Filename conventions (8.3 space padding,
+case folding, the 0x05/0xE5 deleted-entry dance) are deliberately **out of
+scope** and left to consumers.
+
+## Consumers
+
+Designed to be shared by `fsinspect` and friends via path (and later git)
+dependency.
+
+## License
+
+MIT