[derechopiano]

Typing £5 now stores numeric 5 with pound formatting, so =A1*2 produces 10. The existing dollar parser also recognizes pounds in negative/grouped amounts and numeric-text arithmetic; apostrophe-prefixed input remains text.

A separate follow-up commit repairs the failures also present in upstream main CI:

• CSV/TSV export preserves up to 15 significant digits for General-format numbers instead of rounding them to the grid's 11-character display budget. Explicit currency, date and scientific formats still apply. The original CSV tests remain unchanged; the displayed-value test additionally covers a long number, a precise decimal and an explicit scientific format.
• Add the missing French translations for “Different First Page” and “Different Odd & Even Pages”, satisfying the existing translation completeness test.

Validation:

• Pound parsing and engine regressions cover numeric values, arithmetic, display, negative/grouped input, deliberate text, malformed input and XLSX save/reopen. UK-local entry was compared through FormulaLocal in Windows Excel 16.0 build 20326 using an unsaved synthetic workbook.
• Full cargo xtask ci passes locally: all eight gates, 1,330 tests passed and one existing ignored test. No test filters or new exclusions. Generated-file checks ran on LF files, matching the committed files and Linux CI.

No Excel-produced files or assets are included. This extends the existing input syntax; it does not implement a complete locale-dependent parser.
Related work: #447 — regional formats adds region-dependent currency parsing and overlaps this PR's shared input parser. This PR accepts pounds alongside the existing dollar syntax independently of region; it should be reconciled with #447 rather than treated as universal Excel currency-recognition behaviour. Further euro/yen support belongs in that regional-design discussion.

[derechopiano]

Closing as overlapping with the region-aware currency parsing proposed in #447 and the CSV precision and French-label repairs proposed in #449.