fix: actually commit mypy.ini exclude pattern fix (was reverted/never applied)

Previous attempt to fix the (?x) regex parse error was not committed
correctly. Re-applying: exclude now uses plain pipe-separated pattern
compatible with mypy 2.x's INI parser.

mypy.ini

@@ -1,37 +1,19 @@
 [mypy]
-# MyPy configuration for VeriFile-X
-
 python_version = 3.11
-
-# Import discovery
 mypy_path = backend
 namespace_packages = True
-
-# Error reporting
 show_error_codes = True
 show_error_context = True
 show_column_numbers = True
 pretty = True
-
-# Strictness (start lenient, tighten over time)
 ignore_missing_imports = True
 no_implicit_optional = True
 warn_redundant_casts = True
 warn_unused_ignores = True
 warn_return_any = False
 warn_unreachable = True
+exclude = venv/|\.venv/|build/|dist/|\.pytest_cache/|__pycache__/
 
-# Exclude patterns
-exclude = (?x)(
-    ^venv/
-    | ^\.venv/
-    | ^build/
-    | ^dist/
-    | ^\.pytest_cache/
-    | ^__pycache__/
-)
-
-# Per-module options
 [mypy-backend.tests.*]
 ignore_errors = True