build: let uv track git version changes; copy full checkout in Docker

Add uv cache-keys for the commit and tags so the editable install is
refreshed when the git state changes, and copy the complete checkout
(with .git) into the builder so setuptools-scm sees a clean worktree.
Previously the partial copy made git describe report a dirty tree and
tagged Docker builds got a development version suffix.

pyproject.toml

@@ -25,3 +25,10 @@ version_file = "src/xmcp/_version.py"
 
 [tool.setuptools_scm.tag]
 prefix = "release/"
+
+[tool.uv]
+# setuptools-scm derives the version from git; make uv notice commit/tag changes.
+cache-keys = [
+    { file = "pyproject.toml" },
+    { git = { commit = true, tags = true } },
+]