fix: pin black to 26.3.1 across all environments

- Pin black version in requirements-dev.txt (was >=24.0.0)
- Update pre-commit to use black 26.3.1 with Python 3.12
- Add language_version: python3.12 to pre-commit black hook
- Reformat files with new black version for consistency

.pre-commit-config.yaml

@@ -3,7 +3,7 @@
 repos:
   # Ruff - fast Python linter
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.11.2
+    rev: v0.15.8
     hooks:
       - id: ruff
         args: [--fix, --exit-non-zero-on-fix]
@@ -11,10 +11,11 @@ repos:
 
   # Black - Python formatter
   - repo: https://github.com/psf/black
-    rev: 25.1.0
+    rev: 26.3.1
     hooks:
       - id: black
         files: ^(app|tests|scripts)/
+        language_version: python3.12
 
   # Type checking with mypy (optional, slower)
   # Uncomment to enable: