fix: Add --no-must-find-files to cspell to fix false failures

When cspell checks files in batches and all files in a batch are
excluded by ignorePaths, it returns exit code 1 (no files found).
The --no-must-find-files flag suppresses this error for empty batches.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: zah

nix/pre-commit.nix

@@ -55,7 +55,7 @@
     cspell = {
       enable = true;
       name = "cspell (cached)";
-      entry = "cspell --no-progress --cache --config .cspell.json";
+      entry = "cspell --no-progress --cache --no-must-find-files --config .cspell.json";
       language = "system";
       pass_filenames = true;
       files = "\\.(md)$";