fix(skill/command): add user_message param to skill tool, fix command priority order

- BUG-20: Add optional user_message parameter to skill tool for command arguments
- BUG-19: Reorder command discovery: user > project > opencode-project > opencode-global > builtin
- Update AGENTS.md to reflect slashcommand removal and skill tool changes

src/tools/slashcommand/command-discovery.ts

@@ -76,10 +76,10 @@ export function discoverCommandsSync(directory?: string): CommandInfo[] {
   }))
 
   return [
-    ...builtinCommands,
-    ...opencodeProjectCommands,
-    ...projectCommands,
-    ...opencodeGlobalCommands,
     ...userCommands,
+    ...projectCommands,
+    ...opencodeProjectCommands,
+    ...opencodeGlobalCommands,
+    ...builtinCommands,
   ]
 }