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

script/build-schema-document.ts

@@ -9,7 +9,7 @@ export function createOhMyOpenCodeJsonSchema(): Record<string, unknown> {
 
   return {
     $schema: "http://json-schema.org/draft-07/schema#",
-    $id: "https://raw.githubusercontent.com/code-yeongyu/oh-my-opencode/dev/assets/oh-my-opencode.schema.json",
+    $id: "https://raw.githubusercontent.com/code-yeongyu/oh-my-openagent/dev/assets/oh-my-opencode.schema.json",
     title: "Oh My OpenCode Configuration",
     description: "Configuration schema for oh-my-opencode plugin",
     ...jsonSchema,