feat: add OpenCode, Slate, and Cursor host configs

Three new hosts added to the declarative config system. Each is a typed
HostConfig object with paths, frontmatter rules, and path rewrites.
All generate valid SKILL.md output with zero .claude/skills path leakage.

- hosts/opencode.ts: OpenCode (opencode.ai), skills at ~/.config/opencode/
- hosts/slate.ts: Slate (Random Labs), skills at ~/.slate/
- hosts/cursor.ts: Cursor, skills at ~/.cursor/
- .gitignore: add .kiro/, .opencode/, .slate/, .cursor/, .openclaw/

Zero code changes needed — just config files + re-export in index.ts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hosts/opencode.ts

@@ -0,0 +1,46 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const opencode: HostConfig = {
+  name: 'opencode',
+  displayName: 'OpenCode',
+  cliCommand: 'opencode',
+  cliAliases: [],
+
+  globalRoot: '.config/opencode/skills/gstack',
+  localSkillRoot: '.opencode/skills/gstack',
+  hostSubdir: '.opencode',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description'],
+    descriptionLimit: null,
+  },
+
+  generation: {
+    generateMetadata: false,
+    skipSkills: ['codex'],
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '~/.config/opencode/skills/gstack' },
+    { from: '.claude/skills/gstack', to: '.opencode/skills/gstack' },
+    { from: '.claude/skills', to: '.opencode/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 opencode;