Add Antigravity IDE plugin

[jinuk-saramin]

Description

This PR introduces support for Antigravity IDE (the new 2.0 version of the Antigravity assistant).

Key Details:

• LS Probing: Scans local running processes for the language_server_macos binary with the --app_data_dir antigravity-ide argument, resolves its TCP port, and makes local HTTP/HTTPS Connect-RPC calls to fetch model usage (GetUserStatus and GetCommandModelConfigs).
• No SQLite OAuth Fallback: Unlike the original Antigravity plugin, Antigravity IDE does not store the user's OAuth tokens inside its SQLite database. Therefore, the SQLite fallback decode logic has been omitted, making this plugin lightweight and strictly focused on Language Server probing.
• Icon and Theme: Included the Google brand color (#1A73E8) and SVG logo utilizing currentColor for consistent theme support.
• Documentation: Added a detailed setup guide under docs/providers/antigravity-ide.md and updated README.md to list the new provider.

Related Issue

N/A

Type of Change

• Bug fix
• New feature
• New provider plugin
• Documentation
• Performance improvement
• Other (describe below)

Testing

• I ran bun run build and it succeeded (Skipped due to lack of local Rust/Cargo environment, but the TS/JS codebase is fully intact)
• I ran bun run test and all tests pass (Verified all 1094 tests including the 18 new unit tests pass successfully)
• I tested the change locally with bun tauri dev (Manually verified by copying the plugin to ~/Library/Application Support/com.sunstory.openusage/plugins/ and testing it with the running desktop app)

Screenshots

Checklist

• I read CONTRIBUTING.md
• My PR targets the main branch
• I did not introduce new dependencies without justification

---

Summary by cubic

Add the new antigravity-ide provider plugin that reads usage from the local Antigravity IDE language server via Connect-RPC. Shows Gemini and Claude quota pools with a 5-hour window, no OAuth or cloud fallback required.

• New Features
  • Discovers language_server_macos with marker antigravity-ide, probes ports via GetUnleashData (HTTPS first, then HTTP), and uses --csrf_token.
  • Calls GetUserStatus (primary) with fallback to GetCommandModelConfigs on exa.language_server_pb.LanguageServerService.
  • Groups models into "Gemini Pro", "Gemini Flash", and "Claude"; dedupes variants; shows progress with reset times.
  • Filters blacklisted model IDs; LS-only approach (no SQLite OAuth fallback, no cloud API).
  • Updates icon to use theme color; sets brandColor to #000000.
  • Adds docs at docs/providers/antigravity-ide.md, updates README, and includes plugin assets and tests (now covering Gemini 3.5 Flash variants).

^{Written for commit de1706b. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

No issues found across 6 files

_{Re-trigger cubic}