fix: bundled supabase-plugin.tar.gz tarball release

[Rodriguespn]

Summary

The Gemini CLI extension installation via Github releases was failing after migrating to supabase-community/supabase-plugin because the new release contains 5 vendor archives, and the Gemini CLI asset selection logic can't identify the correct one.
Note: installation still works when the CLI clones the GitHub repo directly.

Screen.Recording.2026-06-05.at.19.17.46.mov

This PR bundles all plugin assets into a single supabase-plugin.tar.gz release tarball. With one asset in the release, findReleaseAsset returns it as the generic fallback. Each vendor install finds its own config files inside; Gemini CLI finds gemini-extension.json and ignores the rest.

supabase-plugin.tar.gz
├── .claude-plugin/
│   └── plugin.json
├── .codex-plugin/
│   └── plugin.json
├── .cursor-plugin/
│   └── plugin.json
├── .github/
│   └── plugin/
│       └── plugin.json
├── agents/
│   ├── claude/.mcp.json
│   ├── codex/.app.json
│   ├── copilot/.mcp.json
│   └── cursor/mcp.json
├── assets/
│   └── logo.svg
├── skills/
│   ├── supabase/
│   │   ├── SKILL.md
│   │   ├── assets/feedback-issue-template.md
│   │   └── references/skill-feedback.md
│   └── supabase-postgres-best-practices/
│       ├── SKILL.md
│       └── references/*.md
├── gemini-extension.json
└── SUPABASE.md

How Gemini CLI installs extensions

According to the Gemini CLI extensions docs, the Gemini CLI first checks if there is any GitHub release associated with the repo and, as a fallback, clones the repo and installs the plugin locally.

For the release-based method, findReleaseAsset tries the following asset naming conventions in order:

• Platform and architecture-specific: {platform}.{arch}.{name}.{extension}
• Platform-specific: {platform}.{name}.{extension}
• Generic: A single asset will be used as a fallback if no specific match is found.

The previous repo (supabase-community/gemini-extension) had a single release asset (supabase-gemini-extension.tar.gz), so the generic fallback worked. The new repo (supabase-community/supabase-plugin) publishes 5 assets per release (claude, cursor, codex, copilot, gemini), so none match as the "single asset" generic fallback, causing release-based installation to fail with a 415 error when it falls through to the GitHub source tarball URL.

Closes AI-805

[gregnr]

LGTM