Refresh README and repository About metadata

[Hanjo92]

Summary

• Refresh README copy around current VS Code extension and CLI features.
• Switch the Marketplace package identifier to git-roast-reviewer while keeping the display name as Git Roast.
• Update install instructions for Marketplace and local VSIX installs.
• Update Marketplace category metadata from Source Control to SCM Providers.
• Replace the Marketplace icon with a new flame + Git branch + review check design.
• Bump the extension version to 0.0.13 for the published Marketplace update.

GitHub About

• Updated repository description, homepage, and topics directly on GitHub.
• Homepage now points to the published Marketplace listing.

Marketplace publish

• Published hanjo92.git-roast-reviewer v0.0.13 successfully.
• --skip-duplicate re-run confirmed version 0.0.13 is already published.
• Public listing URL: https://marketplace.visualstudio.com/items?itemName=hanjo92.git-roast-reviewer

Test Plan

• npm run check
• npm audit --omit=dev
• npx vsce verify-pat hanjo92
• npm run package
• npx vsce publish --packagePath git-roast-reviewer-0.0.13.vsix
• npx vsce publish --packagePath git-roast-reviewer-0.0.13.vsix --skip-duplicate
• Visual check of assets/icon.png
• gh repo view Hanjo92/git-roast --json name,description,homepageUrl,repositoryTopics,url,isPrivate

Closes #36
Closes #37
Closes #39