docs: host lists name Copilot, Antigravity and Gemini CLI

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

CONTRIBUTING.md

@@ -736,11 +736,11 @@ worth the review overhead.
 
 ## Multi-host development
 
-gstack generates SKILL.md files for 10 hosts from one set of `.tmpl` templates.
+gstack generates SKILL.md files for 13 hosts from one set of `.tmpl` templates.
 Each host is a typed config in `hosts/*.ts`. The generator reads these configs
 to produce host-appropriate output (different frontmatter, paths, tool names).
 
-**Supported hosts:** Claude (primary), Codex, Factory, Kiro, OpenCode, Slate, Cursor, OpenClaw, Hermes, GBrain.
+**Supported hosts:** Claude (primary), Codex, Factory, Kiro, OpenCode, Slate, Cursor, OpenClaw, Hermes, GBrain, Copilot, Antigravity, Gemini CLI.
 
 ### Generating for all hosts
 
@@ -749,7 +749,7 @@ to produce host-appropriate output (different frontmatter, paths, tool names).
 bun run gen:skill-docs                    # Claude (default)
 bun run gen:skill-docs --host codex       # Codex
 bun run gen:skill-docs --host opencode    # OpenCode
-bun run gen:skill-docs --host all         # All 10 hosts
+bun run gen:skill-docs --host all         # All 13 hosts
 
 # Or use build, which does all hosts + compiles binaries
 bun run build

docs/PROJECT_STRUCTURE.md

@@ -20,6 +20,7 @@ gstack/
 │   ├── codex.ts, factory.ts, kiro.ts  # Existing hosts
 │   ├── opencode.ts, slate.ts, cursor.ts, openclaw.ts  # IDE hosts
 │   ├── hermes.ts, gbrain.ts  # Agent runtime hosts
+│   ├── copilot.ts, agy.ts, gemini.ts  # GitHub Copilot CLI, Antigravity CLI, Gemini CLI
 │   └── index.ts     # Registry: exports all, derives Host type
 ├── scripts/         # Build + DX tooling
 │   ├── gen-skill-docs.ts  # Template → SKILL.md generator (config-driven)