build: derive package version from git via setuptools-scm

Replace hatchling and the static version with setuptools + setuptools-scm,
following Kaya's pre-uv packaging setup: dynamic version, generated
_version.py, and release/* tag prefix. The Docker builder now includes git
and the .git directory so the image is versioned from the checkout. CI
checks out full history and tags for the tag-triggered builds.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "xmcp"
-version = "0.2.0"
+dynamic = ["version"]
 description = "MCP server generated from an OpenAPI specification, built with FastMCP"
 readme = "README.md"
 requires-python = ">=3.14"
@@ -14,8 +14,14 @@ dependencies = [
 xmcp = "xmcp.server:main"
 
 [build-system]
-requires = ["hatchling"]
-build-backend = "hatchling.build"
+requires = ["setuptools>=61.0", "setuptools-scm>=8"]
+build-backend = "setuptools.build_meta"
 
-[tool.hatch.build.targets.wheel]
-packages = ["src/xmcp"]
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.setuptools_scm]
+version_file = "src/xmcp/_version.py"
+
+[tool.setuptools_scm.tag]
+prefix = "release/"