docs: update all GitHub URLs from oh-my-opencode to oh-my-openagent

The GitHub repository was renamed from oh-my-opencode to oh-my-openagent,
but all documentation, scripts, and source code references still pointed
to the old repository name. This caused confusion for users who saw
'oh-my-opencode' in docs but a different repo name on GitHub.

Updated all references across:
- README files (en, ko, ja, zh-cn, ru)
- CONTRIBUTING.md
- docs/ (installation, overview, configuration, etc.)
- Source code (schema URLs, GitHub API calls, issue links)
- Test snapshots

The npm package name remains 'oh-my-opencode' (unchanged).

Fixes: https://x.com/Dhruv14588676/status/2031216617762468348

src/cli/cli-installer.ts

@@ -122,7 +122,7 @@ export async function runCliInstaller(args: InstallArgs, version: string): Promi
 
   console.log(`${SYMBOLS.star} ${color.yellow("If you found this helpful, consider starring the repo!")}`)
   console.log(
-    `  ${color.dim("gh api --silent --method PUT /user/starred/code-yeongyu/oh-my-opencode >/dev/null 2>&1 || true")}`,
+    `  ${color.dim("gh api --silent --method PUT /user/starred/code-yeongyu/oh-my-openagent >/dev/null 2>&1 || true")}`,
   )
   console.log()
   console.log(color.dim("oMoMoMoMo... Enjoy!"))