feat(i18n): RTL layout support (Arabic, Hebrew)

[AimTune]

Goal

Make Chativa render correctly in right-to-left languages (Arabic, Hebrew, Persian, Urdu) so the upcoming `ar` / `he` translations don't ship into a broken layout.

Background

The widget today is hardcoded LTR: message bubbles align left/right by sender, the composer's send button sits on the right, the chat-launcher FAB is positioned bottom-right, and emoji picker / typing indicator / survey screens all assume LTR. Translating strings is necessary but not sufficient — under `dir="rtl"` the layout has to mirror.

Scope

Add RTL support across `@chativa/ui` and `@chativa/genui`. Track translation work in #10.

Detection / wiring

• Maintain a list of RTL languages (`ar`, `he`, `fa`, `ur`) somewhere in core or ui.
• When the active i18next language changes, set `:host([dir]="...")` on the root chat element so all internal CSS can use `[dir="rtl"]` selectors.
• Allow user override via `<chat-iva dir="rtl">` on the host element.

CSS

• Audit every rule using `left` / `right` / `margin-left` / `padding-right` / `text-align: left|right` / `transform: translateX(...)`. Replace with logical properties: `inset-inline-start`, `margin-inline-start`, `text-align: start`, etc.
• Fixed-position overlays (chat-launcher FAB, fullscreen close button, search clear button) must mirror.
• Avatar + bubble alignment: bot on the inline-start, user on the inline-end. (Today this is left/right.)
• Send button + attach button order in the composer must mirror.
• Emoji picker, slash command picker, typing indicator dots, scroll-to-bottom button — all need a pass.
• Survey screen: rating stars rendered LTR even in RTL UIs (this is the conventional rule), but labels and buttons mirror.

Components beyond CSS

• Animations: slide-in / slide-out for the widget panel currently translates X — flip the sign under RTL.
• Virtualized message list (`@lit-labs/virtualizer`) — confirm it handles RTL container correctly; file a workaround if not.
• Markdown links / numbers inside RTL text should render as bidi-isolated (``) where needed.

Tests

• Add a Vitest suite that mounts the widget under `dir="rtl"` and asserts a few key style/layout invariants (e.g. send button is at `inline-end`).
• Manual visual QA: capture sandbox screenshots in EN, AR, HE.

Acceptance

• Switching the language switcher to `ar` (or setting `dir="rtl"`) flips the entire UI cleanly: no half-mirrored components, no overflow into the wrong edge.
• LTR languages render unchanged.
• The fix is structural (logical CSS properties), not a per-language hack.

Notes

• A subset of GenUI components may need their own pass — the built-ins (form, appointment, rating, date picker) should be covered here; user-supplied custom GenUI components are the user's responsibility, but the docs page should call this out.