feat(dispatch): wire marketplace plugin commands into slash command dispatch

Connect the existing plugin loader infrastructure to both slash command
dispatch paths (executor and slashcommand tool), enabling namespaced
commands like /daplug:run-prompt to resolve and execute.

- Add plugin discovery to executor.ts discoverAllCommands()
- Add plugin discovery to command-discovery.ts discoverCommandsSync()
- Add "plugin" to CommandScope type
- Remove blanket colon-rejection error (replaced with standard not-found)
- Update slash command regex to accept namespaced commands
- Thread claude_code.plugins config toggle through dispatch chain
- Add unit tests for plugin command discovery and dispatch

Closes #2019

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Codex <noreply@openai.com>

src/hooks/auto-slash-command/hook.ts

@@ -22,11 +22,15 @@ const sessionProcessedCommandExecutions = new Set<string>()
 
 export interface AutoSlashCommandHookOptions {
   skills?: LoadedSkill[]
+  pluginsEnabled?: boolean
+  enabledPluginsOverride?: Record<string, boolean>
 }
 
 export function createAutoSlashCommandHook(options?: AutoSlashCommandHookOptions) {
   const executorOptions: ExecutorOptions = {
     skills: options?.skills,
+    pluginsEnabled: options?.pluginsEnabled,
+    enabledPluginsOverride: options?.enabledPluginsOverride,
   }
 
   return {