i18n: RTL readiness + text-expansion robustness (R-48)

[ChelseaKR]

Make the PWA RTL-ready, locale-format-correct, and tolerant of text
expansion ahead of new language bundles.

• app/styles.css: convert remaining physical-direction properties to
  logical ones (skip-link left -> inset-inline-start, result list
  padding-left -> padding-inline-start); add wrap tolerance
  (white-space: normal / overflow-wrap / flex-wrap) to buttons, badges,
  and language labels so long localized strings wrap at 320px.
• app/app.js: add an RTL_LANGS map and set dir (rtl/ltr) alongside
  lang in setLanguage. Date/number rendering already uses Intl keyed
  to the active language.
• app/index.html: add explicit dir="ltr" default on .
• tests/test_app_i18n.py: guard no physical-direction CSS, that
  setLanguage sets dir beside lang, and a static pseudo-locale
  expansion check that compact-UI labels stay bounded.
• docs: I18N.md G10 DEFERRED -> PARTIAL; localization-guide soften the
  RTL/format cautions (dir set, logical CSS, Intl formats) while keeping
  the native-speaker visual-QA requirement before shipping an RTL bundle.
• docs/research/synthetic-personas-feedback.md: mark R-48 done.

Co-Authored-By: Claude Fable 5 noreply@anthropic.com

---

Backfill PR for a completed roadmap item (roadmap/rtl-readiness-and-text-expansion-robustn-12, 1 commit(s) over main). Part of the portfolio roadmap batch.