Marketplace prep: official icon, CHANGELOG, PUBLISHING guide

[azizbecha]

Summary

Everything needed to publish to the VS Code Marketplace — minus the parts that need an account.

• Official icon — replaced the hand-rolled phone SVG with the agent-device logo mark (purple `#8232FF`) from the upstream docs site. `media/icon.png` is 128×128, mark centered on the brand dark purple `#3b2860` (sampled from `agent-device-banner.jpg`), rendered via sharp. `galleryBanner.color` matches.
• `package.json` metadata: bump `0.0.1` → `0.1.0`; add `icon`, `keywords`, `homepage`, `bugs.url`, `galleryBanner`, `preview: true`; drop `"private": true`; description sharpened to mention "Vitest-style".
• `CHANGELOG.md` (Keep a Changelog) with `[0.1.0] - 2026-05-03` release notes mirroring the README features.
• `PUBLISHING.md` — end-to-end ops guide: publisher creation, PAT setup, `vsce login`, release pipeline, smoke-install, pre-release flag, Open VSX (Cursor / VSCodium / code-server) mirror via `ovsx`, rollback strategy.
• `README.md` — CI badge, MIT badge, links to `LICENSE`, `CHANGELOG.md`, `PUBLISHING.md`.

Open before `vsce publish`

1. Register the `agent-device` publisher (or whatever ID you settle on — could be `callstackincubator`) at https://marketplace.visualstudio.com/manage.
2. Update `package.json` `publisher` to that ID if it changes.
3. Create a Marketplace-Manage PAT and `npx vsce login `.

`PUBLISHING.md` walks through it step by step.

Test plan

• `npm run lint`, `format:check`, `test`, `compile`, `package` all green
• `.vsix` contains `LICENSE.txt`, `changelog.md`, `readme.md`, `media/icon.png`, `package.json` with all marketplace fields
• CI runs the full pipeline on the PR
• Visually confirm the icon renders well at small sizes (extension list, hover preview)