build: switch hooks to prek, check 50/72

prek replaces pre-commit as the hook runner and reads the same
config. A new commit-msg hook in .prek/ rejects subjects over 50
characters, subjects without a module prefix, and body lines over
72 characters. Install the hooks with `uv run prek install`, and run
them with `just lint`.

justfile

@@ -12,6 +12,10 @@ curses *args:
 basic *args:
     uv run pqcli --basic {{args}}
 
+# Run the formatters and linters on all files
+lint:
+    uv run prek run -a
+
 # Run the test suite; extra arguments go to pytest
 test *args:
     uv run pytest {{args}}