New documents follow the system region: A4, centimetres and decimal comma outside the US (#838) (#857)

* #838: new documents follow the system region (A4/cm/decimal comma outside the US)

- geom: Region (from a locale tag; CLDR Letter and US-measurement territories,
  decimal separator), Unit::format_with; parse_measure takes either separator
  and a Unicode minus.
- engine: Session.region (plain value, en-US headless), Session::units()
  (explicit Measurement units choice wins, else the region's),
  blank_document(); file.new blank uses the region's paper; file.options
  takes "region" and units "auto" and reports unitsFromRegion/region.
  Prefs.units is now Option and saved as measurementUnits (old saved values
  were the inch default, not a choice).
- ui: region from WORDCRAFT_REGION, LC_PAPER/LC_MEASUREMENT/LC_NUMERIC, the
  platform locale (browser on the web) and Windows' home location; length
  fields show and read the region's decimal separator (MeasureExt); Size
  menu lists sizes in the measurement unit.
- Tests: engine new_documents_follow_the_region, geom region/format/parse,
  ui length_fields_follow_the_region. Docs: localization parity, roadmap.

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

* Review fixes for #857: keep a measurement unit chosen before the rename

Settings saved before #838 kept the unit under `editing.units`, defaulting to inches. On load,
a value there other than inches was the user's own choice, so it now carries over to
`measurementUnits` (unless that key is already present); inches, junk and non-strings follow
the region. Test: `a_unit_chosen_before_regions_survives_the_rename`.

Also merged main (ROADMAP.md, engine lib.rs re-exports: `blank_document` and main's
`set_system_locale`). The Windows region code (`GlobalizationPreferences::HomeGeographicRegion`)
was cross-checked with clippy -D warnings for x86_64-pc-windows-gnu.

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

* #838 review: saved region choice, Unix conventions apart, the browser's locale

- File › Options › Advanced › Region: Automatic (the system's) or a chosen region, saved with
  the preferences (`Prefs::region`; `file.options {"region": "pl-PL" | "auto"}`). The session
  keeps the platform's region as `system_region`; `Session::region()` is the one in effect.
  Measurement units gains an Automatic entry (follows the region).
- Unix: numbers follow LC_NUMERIC (else LANG), paper LC_PAPER and measurement LC_MEASUREMENT,
  each on its own (`Region::with_paper_and_measurement`); WORDCRAFT_REGION and LC_ALL still set
  all three.
- Web: sys-locale's `js` feature, so the browser's language reaches the region (and the
  interface language, as its comment already said).
- Runs without preferences (WORDCRAFT_NO_PREFS) stay en-US unless WORDCRAFT_REGION is set.
- docs/localization-parity.md: where the region comes from, the Windows home location vs. Word's
  regional format, and where the decimal separator comes from.

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

* #838 review: rustfmt

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

* #838: rustfmt after merging main

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

* i18n: Hungarian and French strings for this change

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

---------

Co-authored-by: Dmitrii Khlapov <19991457+dkhlapov@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

Cargo.lock

@@ -3847,7 +3847,10 @@ version = "0.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8eab9a99a024a169fe8a903cf9d4a3b3601109bcc13bd9e3c6fff259138626c4"
 dependencies = [
+ "js-sys",
  "libc",
+ "wasm-bindgen",
+ "web-sys",
 ]
 
 [[package]]