chore: add PEP 621 classifiers to pyproject.toml

The PyPI listing for openarmature 0.5.0 currently has no classifiers,
which means:

- The pypi/pyversions Shields.io badge reads empty and renders
  "missing" (the README's python badge was swapped to a dynamic-
  TOML one reading requires-python directly as a workaround).
- PyPI's listing page doesn't show Python compatibility or
  development status in the sidebar.
- PyPI search filters can't find the package by Python version,
  development status, or topic.

Add the standard PEP 621 classifier set:

- Development Status :: 3 - Alpha (matches pre-1.0 framing).
- Programming Language :: Python :: 3 / 3 :: Only / 3.12 (matches
  requires-python = ">=3.12").
- Typing :: Typed (the package ships py.typed at
  src/openarmature/py.typed).
- Intended Audience :: Developers, Operating System :: OS
  Independent, Topic :: Software Development :: Libraries ::
  Python Modules.

No License :: classifier because the project uses the modern SPDX
license-expression field (license = "Apache-2.0"); PyPI rejects
packages that set both forms.

Verified: uv build produces a wheel with all eight classifiers in
METADATA and License-Expression preserved.

Takes effect on the next release to PyPI.

Author: chris-colinsky

pyproject.toml

@@ -11,6 +11,16 @@ requires-python = ">=3.12"
 authors = [{ name = "Chris Colinsky", email = "chris@lunarcommand.xyz" }]
 license = "Apache-2.0"
 license-files = ["LICENSE"]
+classifiers = [
+    "Development Status :: 3 - Alpha",
+    "Intended Audience :: Developers",
+    "Operating System :: OS Independent",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3 :: Only",
+    "Programming Language :: Python :: 3.12",
+    "Topic :: Software Development :: Libraries :: Python Modules",
+    "Typing :: Typed",
+]
 dependencies = [
     "pydantic>=2.7",
     "httpx>=0.27",