fix(installer): actually upgrade pinned plugin version instead of preserving old entry

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/cli/config-manager/add-plugin-to-opencode-config.ts

@@ -79,12 +79,8 @@ export async function addPluginToOpenCodeConfig(currentVersion: string): Promise
 
     const normalizedPlugins = [...otherPlugins]
 
-    if (canonicalEntries.length > 0) {
-      normalizedPlugins.push(canonicalEntries[0])
-    } else if (legacyEntries.length > 0) {
-      const versionMatch = legacyEntries[0].match(/@(.+)$/)
-      const preservedVersion = versionMatch ? versionMatch[1] : null
-      normalizedPlugins.push(preservedVersion ? `${PLUGIN_NAME}@${preservedVersion}` : pluginEntry)
+    if (canonicalEntries.length > 0 || legacyEntries.length > 0) {
+      normalizedPlugins.push(pluginEntry)
     } else {
       normalizedPlugins.push(pluginEntry)
     }