Restore setuptools_scm dynamic versioning reverted by SDK regeneration

The SDK regeneration in #45 reverted the PLAT-193 fix (a1fa54f):
pyproject.toml went back to a hardcoded version = "1.0.0", so every tag
push built opal_security-1.0.0, which already exists on PyPI, and
twine --skip-existing silently skipped the upload. Re-apply the fix
(dynamic version via setuptools_scm) and add pyproject.toml to
.openapi-generator-ignore so regeneration cannot revert it again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ssy8nmvQp1U5d73pCMFNXi

Author: claude

.openapi-generator-ignore

@@ -21,3 +21,8 @@
 #docs/*.md
 # Then explicitly reverse the ignore rule for a single file:
 #!docs/README.md
+
+# pyproject.toml is hand-maintained: it uses setuptools_scm dynamic versioning
+# (PLAT-193) so releases derive their version from git tags. Regenerating it
+# would revert to a hardcoded version and silently break PyPI publishing.
+pyproject.toml

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "opal_security"
-version = "1.0.0"
+dynamic = ["version"]
 description = "Opal API"
 authors = [
   {name = "Opal Team",email = "hello@opal.dev"},
@@ -32,7 +32,7 @@ mypy = ">= 1.5"
 
 
 [build-system]
-requires = ["setuptools"]
+requires = ["setuptools", "setuptools_scm"]
 build-backend = "setuptools.build_meta"
 
 [tool.pylint.'MESSAGES CONTROL']