chore: v2.8.7 — Git SSH keys in tabs, safer Artifacts preview and search

- Settings → Git → Your git identity: SSH keys are one tab per host kind
  (GitHub · GitLab, AWS CodeCommit, More keys, Other hosts); opens on the
  AWS tab when only an RSA key exists.
- Artifacts: a file type the sandboxed preview cannot show (Office, zip,
  PDF) offers Download only, never a blank Preview.
- Artifacts search: `%`/`_`/`\` in a query match literally (LIKE ... ESCAPE).
- Skill frontmatter rewrite replaces a key with its continuation lines and
  quotes values YAML could misread.
- Plugin marketplace.json is read with a 1 MB streaming cap.
- Artifact lists look each owner up once.

client/src/i18n/locales/en/artifacts.json

@@ -32,6 +32,7 @@
   "copyLink": "Copy link",
   "preview": "Preview",
   "download": "Download",
+  "noPreview": "This file type cannot be shown here — download it to open it.",
   "install": "Install",
   "installs": "{{count}} installs",
   "installed": "Installed to {{path}}",