fix(shared): merge project and user opencode plugin detection

Stop dropping user-level plugin conflicts when an empty project config exists by collecting plugin entries from every supported OpenCode config path.

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

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

src/shared/load-opencode-plugins.ts

@@ -0,0 +1,58 @@
+import * as fs from "node:fs"
+import * as os from "node:os"
+import * as path from "node:path"
+
+import { parseJsoncSafe } from "./jsonc-parser"
+
+interface OpencodeConfig {
+  plugin?: string[]
+}
+
+function getWindowsAppdataDir(): string | null {
+  return process.env.APPDATA || null
+}
+
+function getConfigPaths(directory: string): string[] {
+  const crossPlatformDir = path.join(os.homedir(), ".config")
+  const paths = [
+    path.join(directory, ".opencode", "opencode.json"),
+    path.join(directory, ".opencode", "opencode.jsonc"),
+    path.join(crossPlatformDir, "opencode", "opencode.json"),
+    path.join(crossPlatformDir, "opencode", "opencode.jsonc"),
+  ]
+
+  if (process.platform === "win32") {
+    const appdataDir = getWindowsAppdataDir()
+    if (appdataDir) {
+      paths.push(path.join(appdataDir, "opencode", "opencode.json"))
+      paths.push(path.join(appdataDir, "opencode", "opencode.jsonc"))
+    }
+  }
+
+  return paths
+}
+
+export function loadOpencodePlugins(directory: string): string[] {
+  const pluginEntries: string[] = []
+  const seenPluginEntries = new Set<string>()
+
+  for (const configPath of getConfigPaths(directory)) {
+    try {
+      if (!fs.existsSync(configPath)) continue
+
+      const content = fs.readFileSync(configPath, "utf-8")
+      const result = parseJsoncSafe<OpencodeConfig>(content)
+      const plugins = result.data?.plugin ?? []
+
+      for (const plugin of plugins) {
+        if (seenPluginEntries.has(plugin)) continue
+        seenPluginEntries.add(plugin)
+        pluginEntries.push(plugin)
+      }
+    } catch {
+      continue
+    }
+  }
+
+  return pluginEntries
+}