fix: promote CLAUDE.md to main template when group becomes main

When a non-main group is re-registered with --is-main, the existing
CLAUDE.md (copied from global template) lacked admin context. Now
register.ts detects this promotion case and replaces it with the main
template. Files that already contain "## Admin Context" are preserved.

Adds tests for:
- promoting non-main to main upgrades the template
- cross-channel promotion (e.g. Telegram non-main → main)
- promotion with custom assistant name
- re-registration preserves user-modified main CLAUDE.md
- re-registration preserves user-modified non-main CLAUDE.md

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

setup/register.ts

@@ -116,7 +116,7 @@ export async function run(args: string[]): Promise<void> {
     recursive: true,
   });
 
-  // Create CLAUDE.md in the new group folder from template if it doesn't exist.
+  // Create or upgrade CLAUDE.md in the group folder from the appropriate template.
   // The agent runs with CWD=/workspace/group and loads CLAUDE.md from there.
   const groupClaudeMdPath = path.join(
     projectRoot,
@@ -124,15 +124,30 @@ export async function run(args: string[]): Promise<void> {
     parsed.folder,
     'CLAUDE.md',
   );
-  if (!fs.existsSync(groupClaudeMdPath)) {
-    const templatePath = parsed.isMain
-      ? path.join(projectRoot, 'groups', 'main', 'CLAUDE.md')
-      : path.join(projectRoot, 'groups', 'global', 'CLAUDE.md');
+  const mainTemplatePath = path.join(projectRoot, 'groups', 'main', 'CLAUDE.md');
+  const globalTemplatePath = path.join(projectRoot, 'groups', 'global', 'CLAUDE.md');
+  const templatePath = parsed.isMain ? mainTemplatePath : globalTemplatePath;
+  const fileExists = fs.existsSync(groupClaudeMdPath);
+
+  // Promotion case: group was registered as non-main (got global template)
+  // and is now being re-registered as main. Replace with main template.
+  const needsPromotion =
+    parsed.isMain &&
+    fileExists &&
+    !fs.readFileSync(groupClaudeMdPath, 'utf-8').includes('## Admin Context');
+
+  if (!fileExists || needsPromotion) {
     if (fs.existsSync(templatePath)) {
       fs.copyFileSync(templatePath, groupClaudeMdPath);
       logger.info(
-        { file: groupClaudeMdPath, template: templatePath },
-        'Created CLAUDE.md from template',
+        {
+          file: groupClaudeMdPath,
+          template: templatePath,
+          promoted: needsPromotion,
+        },
+        needsPromotion
+          ? 'Promoted CLAUDE.md to main template'
+          : 'Created CLAUDE.md from template',
       );
     }
   }