feat: add Copilot host configuration and update .gitignore

.gitignore

@@ -15,6 +15,7 @@ bin/gstack-global-discover
 .opencode/
 .slate/
 .cursor/
+.copilot/
 .openclaw/
 .hermes/
 .gbrain/

hosts/copilot.ts

@@ -0,0 +1,46 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const copilot: HostConfig = {
+  name: 'copilot',
+  displayName: 'GitHub Copilot',
+  cliCommand: 'copilot',
+  cliAliases: ['gh-copilot', 'copilot-cli'],
+
+  globalRoot: '.copilot/skills/gstack',
+  localSkillRoot: '.copilot/skills/gstack',
+  hostSubdir: '.copilot',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description', 'triggers', 'platforms'],
+    descriptionLimit: 1024,
+    descriptionLimitBehavior: 'truncate',
+  },
+
+  generation: {
+    generateMetadata: false,
+    metadataFormat: null,
+    skipSkills: ['codex'],
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '~/.copilot/skills/gstack' },
+    { from: '.claude/skills/gstack', to: '.copilot/skills/gstack' },
+    { from: '.claude/skills', to: '.copilot/skills' },
+  ],
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
+    globalFiles: { 'review': ['checklist.md', 'TODOS-format.md'] },
+  },
+
+  install: {
+    prefixable: false,
+    linkingStrategy: 'symlink-generated',
+  },
+
+  learningsMode: 'basic',
+};
+
+export default copilot;