Give dynamic versioning a fallback for git-less builds

The Docker build copies only pyproject.toml and rmcp/ (.dockerignore
excludes .git), so hatchling had no repository to read a tag from:

  RuntimeError: Error getting the version from source
  `uv-dynamic-versioning`: This does not appear to be a Git project

That failed the image build, which in turn skipped r-testing,
docker-scenarios and production-container-tests -- the same dependency
chain that hid the R suite last time.

fallback-version keeps git-less builds working. It cannot mask a bad
release: release builds run in a full checkout with fetch-depth 0, and
the publish workflow asserts the built version matches the tag, so a
fallback reaching PyPI would fail the guard rather than upload 0.0.0.

Reproduced locally by building from a copy of just pyproject.toml and
rmcp/, which is what the Docker context actually contains.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: soodoku

pyproject.toml

@@ -96,6 +96,12 @@ source = "uv-dynamic-versioning"
 [tool.uv-dynamic-versioning]
 vcs = "git"
 style = "pep440"
+# The Docker build copies only pyproject.toml and rmcp/ (.dockerignore
+# excludes .git), so there is no repository to read a tag from. Without a
+# fallback the backend raises "This does not appear to be a Git project" and
+# the image build fails. Release builds run in a full checkout and derive the
+# real version from the tag; the publish workflow asserts that it matches.
+fallback-version = "0.0.0"
 
 # Flat layout: the package lives at the repo root, not under src/.
 [tool.hatch.build.targets.wheel]