Migrate to pyproject.toml with setuptools_scm

Replace custom version management with setuptools_scm to eliminate
source file modifications during installation. Version is now derived
from git tags at build time without writing to tracked files.

Changes:
- Add pyproject.toml with full project metadata
- Simplify setup.py to minimal backwards-compatible shim
- Remove curateipsum/_version.py from version control
- Add _version.py to .gitignore (auto-generated at build time)
- Use PEP 440 compliant version strings

Fixes #18

.gitignore

@@ -25,6 +25,9 @@ wheels/
 *.egg
 MANIFEST
 
+# Version file generated by setuptools_scm
+curateipsum/_version.py
+
 # PyInstaller
 #  Usually these files are written by a python script from a template
 #  before PyInstaller builds the exe, so as to inject date/other infos into it.
@@ -72,8 +75,9 @@ target/
 # Jupyter Notebook
 .ipynb_checkpoints
 
-# pyenv
+# uv
 .python-version
+uv.lock
 
 # celery beat schedule file
 celerybeat-schedule