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/hooks/directory-agents-injector/finder.ts

@@ -18,7 +18,7 @@ export function findAgentsMdUp(input: {
 
   while (true) {
     // Skip root AGENTS.md - OpenCode's system.ts already loads it via custom()
-    // See: https://github.com/code-yeongyu/oh-my-opencode/issues/379
+    // See: https://github.com/code-yeongyu/oh-my-openagent/issues/379
     const isRootDir = current === input.rootDir;
     if (!isRootDir) {
       const agentsPath = join(current, AGENTS_FILENAME);