chore: v2.8.13 — Artifacts reinstall/edit/installs, agent steps in chat, pick a local file to attach, Windows paths as links

- Chat: an Agent step shows its task, status and tool calls and opens its conversation in place; Windows paths (E:\…, C:/…) in replies open as files
- Prompt: attach a file on this computer by path (native picker), clearer too-large messages
- Artifacts: edit title/description and a skill's files (new snapshot), Reinstall, install history, Hub-only rows, skills installed into ~/.claude/skills and ~/.agents/skills
- Files: batch upload of small files in one extract
- AI Tools: npm install falls back to --prefix ~/.local when the global prefix is not writable

server/data/ai-tools/antigravity.json

@@ -20,6 +20,10 @@
   ],
   "homepageUrl": "https://antigravity.google/docs/cli/overview",
   "faviconDomain": "antigravity.google",
+  "install": {
+    "kind": "script",
+    "url": "https://antigravity.google/cli/install.sh"
+  },
   "config": [
     {
       "path": "~/.gemini/GEMINI.md"