docs: add RTL development skill (#40543)

.opencode/skills/rtl-aware-development/SKILL.md

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+---
+name: rtl-aware-development
+description: OpenCode Desktop should be RTL-aware. Use when implementing or reviewing RTL/LTR behavior in the web app, desktop app, CSS, menus, scrolling, resizing, icons, mixed-direction text, or Electron title bars.
+---
+
+# RTL-Aware Development
+
+Treat direction as independent from language. Test English in both directions as well as real RTL and mixed-script content.
+
+## Guidelines
+
+- Set `lang` and `dir` on the document, and propagate direction through component providers used by portaled menus and popovers. Do not change the selected locale merely to force RTL.
+- Keep DOM and focus order semantic. Flexbox and Grid already follow `dir`; do not add `row-reverse`, CSS `order`, or reversed markup just to mirror a layout.
+- Prefer logical CSS for semantic layout. Reserve physical coordinates for pointer positions, canvas geometry, native window controls, and other genuinely physical placement.
+
+```css
+/* Avoid */
+padding-left: 12px;
+right: 0;
+border-right: 1px solid;
+text-align: left;
+
+/* Prefer */
+padding-inline-start: 12px;
+inset-inline-end: 0;
+border-inline-end: 1px solid;
+text-align: start;
+```
+
+- Isolate mixed-direction text. Use `dir="auto"` or `<bdi>` for unknown text; keep code, URLs, IDs, and filesystem paths LTR without forcing the surrounding component LTR.
+
+```html
+<span class="file-row"><bdi dir="auto">README.md</bdi></span> <bdi dir="ltr"><code>C:\src\app.ts</code></bdi>
+```
+
+- Mirror directional meaning, not every image. Back/forward, previous/next, disclosure, indentation, and directional progress may need mirroring. Do not mirror brands, clocks, media controls, charts, or text. Reverse physical gradients, `translateX`, SVG transforms, and animation deltas explicitly.
+- Map interactions through direction. `clientX` remains physical; resizing a logical edge needs an RTL-aware delta. Logical previous/next keyboard controls may swap ArrowLeft/ArrowRight. Follow the relevant WAI-ARIA widget pattern.
+- Do not assume LTR scrolling. RTL `scrollLeft` can start at `0` and become negative. Prefer `scrollIntoView({ inline: "nearest" })` or a tested direction-normalizing helper.
+- For Electron title bars, prefer native caption controls and use `titleBarOverlay` plus `env(titlebar-area-*)` for the safe content rectangle. Keep Windows/macOS native-control avoidance and `trafficLightPosition` physical; keep app navigation inside that rectangle logical. Mark interactive titlebar children `app-region: no-drag`.
+- Verify behavior, not screenshots alone. Check computed styles, pseudo-element geometry, hit zones, focus order, keyboard behavior, submenu direction, zoom/scaling, and both LTR and RTL scroll endpoints.
+
+## Test Matrix
+
+- English + LTR
+- English + forced RTL
+- A real RTL locale + RTL
+- Mixed RTL/LTR content, long labels, numbers, code, and paths
+- Keyboard, pointer resize, scrolling, menus/submenus, and Electron titlebar controls in both directions
+
+## References
+
+- [RTL Styling 101, Ahmad Shadeed](https://rtlstyling.com/posts/rtl-styling/)
+- [CSS-Tricks: RTL Styling 101](https://css-tricks.com/rtl-styling-101/)
+- [CSS-Tricks: CSS Logical Properties and Values](https://css-tricks.com/css-logical-properties-and-values/)
+- [W3C: Structural markup and right-to-left text](https://www.w3.org/International/questions/qa-html-dir)
+- [W3C: Inline bidirectional markup](https://www.w3.org/International/articles/inline-bidi-markup/)
+- [MDN: CSS logical properties and values](https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Logical_properties_and_values)
+- [MDN: `dir`](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Global_attributes/dir)
+- [MDN: `scrollLeft`](https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollLeft)
+- [web.dev: Logical properties](https://web.dev/learn/css/logical-properties/)
+- [Electron: Custom title bar](https://www.electronjs.org/docs/latest/tutorial/custom-title-bar)
+- [WAI-ARIA: Window splitter pattern](https://www.w3.org/WAI/ARIA/apg/patterns/windowsplitter/)
+- [Kobalte: I18n Provider](https://kobalte.dev/docs/core/components/i18n-provider/)