Antigravity 2.0 Custom Subagents not surfaced — `templateContext.agentCapable` still false in 0.7.0-beta.4

Antigravity 2.0 natively supports custom subagents (Markdown + YAML frontmatter, workspace discovery at .agents/agents/<name>.md, parent dispatch via invoke_subagent), but Trellis still emits no agent files for the platform: AI_TOOLS.antigravity.templateContext.agentCapable is false in dist/types/ai-tools.js (verified against the 0.7.0-beta.4 package source; zcode/snow are true), and dist/configurators/antigravity.js only produces .agent/workflows/ + .agent/skills/. The bundled platform-map also lists Antigravity under "Main-Session Workflow Platforms" (agent dir "Usually none").

This forces per-repo workarounds (hand-written agent files referencing role-contract skills) and blocks contract-layer registration (e.g. REQUIRED_PLATFORMS validation on top of the emitted agent files).

Related: #592 (full Antigravity CLI support), #349 (platform support tracking).

Request: set agentCapable: true and emit agent-file templates for Antigravity 2.0+. Happy to share our working local setup (.agents/agents/trellis-{research,implement,check,critic}.md patterns) as reference.

Environment: trellis init --antigravity, @mindfoldhq/trellis 0.7.0-beta.1 verified against 0.7.0-beta.4 package source.