Changed PACKAGE_NAME from 'oh-my-openagent' to 'oh-my-opencode' in
auto-update-checker/constants.ts to match package.json. This fixes
getCachedVersion() returning null, causing 'unknown' in version toast.
TDD: red-green confirmed. 39 tests pass, tsc clean.
Closes#3129
Align version lookup, invalidation, and bun install with OpenCode's cache directory so updates target the loaded plugin location. Keep dependency declarations intact during invalidation so auto-update can reinstall instead of converging to uninstall.