feat: Rename application from "Codewalk District" to "Codewalkers"

Update all user-facing strings (HTML title, manifest, header logo,
browser title updater), code comments, and documentation references.
Folder name retained as-is.

apps/server/cli/index.ts

@@ -1,5 +1,5 @@
 /**
- * Codewalk District CLI
+ * Codewalkers CLI
  *
  * Commander-based CLI with help system and version display.
  * Supports server mode via --server flag.