refactor(cli): rename nc to ncl

Rename the CLI binary, socket path, container wrapper, error prefixes,
and all references from `nc` to `ncl`. Add ~/.local/bin symlink during
setup and pnpm script alias.

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

src/cli/registry.ts

@@ -1,5 +1,5 @@
 /**
- * Command registry — single source of truth for what `nc` can do.
+ * Command registry — single source of truth for what `ncl` can do.
  *
  * Each command file under `commands/` calls `register()` at top level,
  * and `commands/index.ts` imports them all for side effects so the