Read cell formatting from .xls files

.xls (Excel 97-2003) import used only each cell's number format. It now
also reads the BIFF8 formatting records (Font, XF, Palette and Style),
so opened sheets keep their fonts, solid and pattern fills, borders
(including diagonals), alignment (rotation, indent, wrap, shrink),
locked and hidden protection, the workbook's custom colour palette, its
Normal font as the default, and its user-defined cell styles.

The decoding lives in a new xls/styles.rs; xls/mod.rs gains the record
arms and the build call. Short or malformed formatting records keep the
fields present and add one warning instead of refusing the workbook.
Tests build the records in code, including truncation and byte mutation.

Also merges origin/main, keeping its dialog-sheet, WINDOW2 and XF
number-format handling; the XF arm now goes through the new styles
module, which covers the number format too.

ROADMAP.md

@@ -148,6 +148,7 @@ Ranked; estimates in Opus 5.5 agent-hours. Detail and the full beta-gate list in
 | 2026-10-15 | Function help follows the interface language: argument hints, autocomplete, Insert Function (search and readable categories) and the Formulas-tab menus read per-language tables of descriptions and argument names; Spanish keeps its 10 functions in the new format |
 | 2026-10-15 | Row auto-fit counts a cell's line breaks only when the cell wraps, as Excel does: a file whose unwrapped cells hold multi-line text no longer opens with tall rows (typing a break still turns wrap on and grows the row) |
 | 2026-10-14 | Protect Sheet on a protected sheet: Home › Format, its keytips (HOP, RPS) and the tab menu now read Unprotect Sheet… and unprotect (straight away without a password); a protected sheet that forbids selecting locked (or unlocked) cells is enforced for clicks, arrows and Go To, and the Protect Sheet dialog has the select options (#1346) |
+| 2026-10-14 | `.xls` (Excel 97-2003) files open with their formatting: fonts, solid and pattern fills, borders (with diagonals), alignment (rotation, indent, wrap, shrink), locked and hidden cells, the workbook's custom colour palette, its Normal font and its user-defined cell styles |
 | 2026-10-14 | XLSX: formulas opened with dynamic-array metadata (`cm`) keep it on save, with `xl/metadata.xml`. Before, a formula returning one value lost it (11 of 40 corpus files that have the part lost it entirely), and Excel recalculated some of them with implicit intersection (`SUMPRODUCT(IFERROR(...))` changed value) |
 | 2026-10-14 | Recalculation: a dynamic array's anchor given a new formula that reads its old spill area (`A1` was `=SEQUENCE(3)`, becomes `=SUM(A2:A3)+1` or `=SEQUENCE(1,A2+1)`) sees that area empty instead of the old values |
 | 2026-10-14 | Recalculation: when two arrays of one recalculation want the same empty cells, the formulas that read the one laid out second (at its anchor or over the cells it would have spilled into) read `#SPILL!` and empty cells instead of its values |
@@ -230,6 +231,7 @@ Ranked; estimates in Opus 5.5 agent-hours. Detail and the full beta-gate list in
 | 2026-10-16 | minor | Progress log: floating pictures' textures bounded and kept per workbook |
 | 2026-10-16 | trivial | Progress log: web preferences kept between visits (#1562) |
 | 2026-10-16 | minor | Progress log: interface fonts held once instead of twice |
+| 2026-10-14 | minor | Progress log: `.xls` import reads cell formatting |
 | 2026-10-14 | minor | XLSX dynamic-array `cm` metadata kept on save; progress log row |
 | 2026-10-14 | minor | Progress log: spill anchor reading its old spill area |
 | 2026-10-14 | minor | Progress log: formulas reading an array that loses a spill conflict |