fix: add --email CLI flag for signup provisioning (#414)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MattBro

bin.ts

@@ -120,6 +120,11 @@ const cli = yargs(hideBin(process.argv))
         'PostHog project ID to use (optional; when not set, uses default from API key or OAuth)\nenv: POSTHOG_WIZARD_PROJECT_ID',
       type: 'string',
     },
+    email: {
+      describe:
+        'Email address for signup (used with --signup)\nenv: POSTHOG_WIZARD_EMAIL',
+      type: 'string',
+    },
   })
   .command(
     ['$0'],