Load remote features.json via ?features=URL（URL 分享：远程 features.json）

[Kaka-cheaper]

Goal

Let the viewer load any URL-accessible features.json via a query parameter, so people can share a link instead of cloning a repo.

Why

Roadmap top item: "Share via URL". Current viewer only loads bundled examples or local files. Adding ?features=<url> and ?repo=<owner>/<repo> makes codeSee viable for showcasing OSS projects, code review sharing, blog embeds.

Scope (what is in)

• Parse ?features=<url> from location.search
• Parse ?repo=<owner>/<repo> shorthand → expand to https://raw.githubusercontent.com/{owner}/{repo}/main/.codesee/features.json
• ?repo=owner/repo@branch for non-main branches
• Fetch with timeout (10s), validate as a FeaturesFile before rendering
• Show source label in TopBar (the host of the URL)
• Error UI: clear message on CORS / 404 / parse failure (don't white-screen)
• Read-only mode: dragging works but layout writes go to localStorage only (no FSA save)
• When ?features= is set, ?example= is ignored

Out of scope

• Authenticated fetches (private repos): user can drag-drop the file instead
• ?layout=URL for layout (do in follow-up issue)
• Embed mode (?embed=1): separate issue

Files likely involved

• viewer/src/App.tsx (parse URL, dispatch to loader)
• viewer/src/fcg/loader.ts (loadFromUrl already exists, may need polish)
• viewer/src/app/TopBar.tsx (source label)

Acceptance criteria

• ?features=https://raw.githubusercontent.com/Kaka-cheaper/codeSee/main/viewer/public/features.json loads and renders
• ?repo=Kaka-cheaper/codeSee does the same via shorthand
• Invalid URL → user-readable error, no white screen
• CORS-blocked URL → message suggests dragging the file instead
• Layout drags persist to localStorage, not FSA

Estimated effort

~3-4 hours / ~3 files

Hints

fetchFromUrl in loader.ts does most of the work. Main delta is URL parsing + the ?repo= expansion + safe error rendering.

Security check

• Don't execute anything from the JSON
• Treat the URL hostname as untrusted
• Validate response < 5MB before parsing

Want to take this?

Comment "I'd like to take this" and I'll confirm within 24h.