Layered TIFF: open and save Photoshop layer data in TIFF files, in either byte order (part of #215) (#672)

* Layered TIFF: open and save Photoshop layer data in TIFF files, in either byte order (part of #215)

Photoshop keeps a layered TIFF's layers in two private tags: 37724 (ImageSourceData, the same
layer section a PSD has) and 34377 (the image resources). PhotoCraft now reads and writes both,
so a TIFF opens with its groups, masks, layer styles, type, shapes, smart objects and adjustment
layers exactly as the PSD path would, and saves them back.

* photocraft-psd: a `tiff` module with `ImageSourceData` (parse/write, PSD- and PSB-sized),
  the 34377 resource helpers, and a field-by-field byte-order transcoder. In Intel-order TIFFs
  Photoshop byte-swaps the whole block structure (reversed keys, little-endian integers and
  doubles) while pixel samples stay big-endian; the transcoder knows the layer-info structure,
  masks, blending ranges and every block photocraft-io maps (descriptors, TySh, lrFX, the
  binary adjustments, paths, patterns, filter effects, metadata settings, linked layers,
  annotations...), recognizes descriptor-shaped unknown blocks, and drops the rest with a
  warning instead of passing byte-swapped data to other readers. The reader gained an optional
  little-endian mode. 23 unit tests; a fuzz target in the CI matrix.
* photocraft-codecs: the two tags travel as opaque bytes on `Metadata`, read by a
  bounds-checked walk of IFD0 (classic and BigTIFF, both byte orders) and written back as
  BYTE / UNDEFINED tags. `tiff_writes_little_endian()` tells which order the encoder produces.
* photocraft-io: `tiff_layers` rebuilds a PSD model from the TIFF's pixels plus the tags on
  import, and on export runs the PSD exporter (new `merged_matte` / `merged_compression`
  options), interleaves its merged planes for the TIFF image and stores the layer section in
  the encoder's byte order. `ExportOptions.tiff_layers` (default on). Lab and Multichannel
  documents save flat; extra alpha channels are not written (one transparency sample).
* UI: the TIFF Options prompt ("Including layers will increase file size." / "Discard Layers
  and Save a Copy" / "Don't show again") behind Preferences > File Handling > Ask Before
  Saving Layered TIFF Files; `ExportSettings.tiff_layers`; catalogs updated.
* Tests: io round trips at 8/16/32 bits in Gray/RGB/CMYK, equivalence with the PSD path, every
  TIFF compression, the flat fall-backs, malformed input, and files written by psdtags in both
  byte orders (fixtures from scripts/layered_tiff_fixtures.py); a corpus test (feature
  `corpus`) writes every corpus PSD as a layered TIFF and compares the result with the PSD
  round trip (700 files, 0 differences, 0 crashes). Codecs tests cover the tag walk on
  hand-made files.
* Scorecard FILE-215-7 done, BUG-204-3 partial; README and book updated.

Co-Authored-By: Claude Mythos 5.1 <noreply@anthropic.com>

* Layered TIFF: de and pt-br strings; neutral wording in the psd tiff docs

The four psdtags fixtures stay out of the repository (no binary test data here): the
generator now writes them to the gitignored corpus/layered-tiff/, and the tests that read
them skip with a message when absent.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Regenerate docs/scorecard.md

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: leon <claude.udder842@passmail.net>
Co-authored-by: Claude Mythos 5.1 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

book/src/formats/raster-formats.md

@@ -2,6 +2,10 @@
 
 `photocraft-codecs` provides format detection, capability declarations, decode limits, metadata handling, and encoding for flat images. The default build declares read/write support for PNG, JPEG, TIFF, WebP, GIF, BMP, TGA, ICO, Netpbm/PFM, QOI, OpenEXR, and Radiance HDR. HEIF/HEIC (iPhone and Mac photos) is read-only, decoded in pure Rust by `heic-rs` through the optional `photocraft-heif` crate. It is a build-time choice behind the `heif` cargo feature (`cargo build -p photocraft --features heif`): official builds include it; without it HEIC files are still recognised and opening one reports that HEIC support isn't included in that build. AVIF encoding is optional; AVIF decoding is not implemented in the current crate.
 
+## Layered TIFF
+
+A TIFF saved by Photoshop with its layers carries them in two private tags: 37724 (`ImageSourceData`, the same layer section a PSD has, preceded by the string `Adobe Photoshop Document Data Block`) and 34377 (the PSD image resources). `photocraft-codecs` passes both through as opaque bytes on `Metadata`; `photocraft-io` rebuilds a PSD model from them plus the TIFF's pixels and hands it to the PSD importer, so groups, masks, layer styles, type, shapes, smart objects and adjustment layers open from a TIFF exactly as from a PSD, and are written back the same way. In Intel-order (`II`) files Photoshop stores the whole block structure byte-swapped (reversed keys such as `MIB8` and `ryaL`, little-endian integers and doubles) while pixel samples stay big-endian; `photocraft-psd`'s `tiff` module converts between the two orders field by field, and drops, with a warning, any block whose layout it does not know rather than pass byte-swapped data to other readers. Limits: a TIFF holds one transparency sample, so extra alpha channels are not written; Lab documents are saved flat. Save As asks "Including layers will increase file size" (with "Discard Layers and Save a Copy") while *Ask Before Saving Layered TIFF Files* is on in Preferences › File Handling.
+
 Capability details such as sample depth, channel layout, alpha, ICC, EXIF, XMP, DPI, and animation behavior are defined by `crates/codecs/src/format.rs`. Do not infer fidelity from the filename extension alone.
 
 ## Exporting documents