✨ feat(harness): add agy coding agent integration

[Skyline-9]

Description

Resolves #223

This PR integrates Google Antigravity (agy) as a first-class coding-agent harness in OpenResearch (orx), alongside Claude Code, OpenAI Codex, OpenCode, and Cursor.

Key Motivation

• Token Quotas & Broad Access: Higher limits on Gemini Pro & Flash tiers, lowering friction for student and academic users running intensive auto-research loops.
• Outreach for Edu: Google has a generous edu plan for gemini, making it more accessible than Claude and Codex for student researchers
• Large Context Window (1M+ Tokens): Essential for full-paper review, arXiv exploration, large benchmark traces, and autonomous loop logs.
• Unified Tooling: Seamless normalization of native tools (run_command, view_file, write_to_file, replace_file_content, list_dir, read_url_content).

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Changes

1. Harness Trait Implementation (src/local/harness/antigravity.rs):

   • Spawns agy --output-format stream-json per turn, folding streaming NDJSON into TurnCtx.
   • Multi-turn conversation continuity with --conversation <conversation_id>.
   • Dynamic model discovery and authentication verification via agy models.
   • Worktree isolation via project cwd and --add-dir.
   • Worktree session skills auto-discovery via .agents/skills.
   • Native options: permission modes (ask, auto, bypass), reasoning effort levels (low, medium, high), and command-based planning mode.
   • Fast one-shot execution (agy_one_shot) for session titling and summaries.

2. Registry & Storage (src/local/harness/mod.rs, src/local/native_store.rs):

   • Registered Antigravity in registry().
   • Added antigravity_home to native storage resolution.

3. Skills Installer (src/commands/install_skills.rs):

   • Added antigravity and agy aliases to orx install-skills --agent <name>.

4. Web UI & Dashboard (ui/src/):

   • Added antigravity to HarnessId in ui/src/api.ts.
   • Added SVG mark for Antigravity in ui/src/components/HarnessLogo.tsx.
   • Added human-readable labels in ui/src/components/ModelPicker.tsx.
   • Rebuilt and committed production bundle assets in ui/dist.

5. Testing:

   • Comprehensive unit tests in antigravity.rs for NDJSON stream folding, tool translation, model list parsing, and error result handling.
   • Integration tests in harness/mod.rs and install_skills.rs passing.
   • Full test suite passing (818 passed; 0 failed).
   • Clean cargo fmt and cargo clippy --all-targets.

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