fix(cli): support project slash command completion (#245)

Add project-level slash command discovery with recursive nested command scanning, pass workingDirectory through slash-command handlers, and align hub/web source unions to include project commands.

web/src/types/api.ts

@@ -151,7 +151,7 @@ export type GitStatusFiles = {
 export type SlashCommand = {
     name: string
     description?: string
-    source: 'builtin' | 'user' | 'plugin'
+    source: 'builtin' | 'user' | 'plugin' | 'project'
     content?: string  // Expanded content for Codex user prompts
     pluginName?: string
 }