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.

.dockerignore

@@ -1,4 +1,3 @@
-.gitignore
 .venv/
 __pycache__/
 *.py[cod]
@@ -7,15 +6,11 @@ __pycache__/
 .mypy_cache/
 .env
 .env.*
-docker-compose*.yml
-Dockerfile
-.dockerignore
-*.md
-!README.md
 xmcp.yml
-xmcp.example.yml
+xmcp.local.yml
 
 # Generated at build time
 src/xmcp/_version.py
 *.egg-info/
+build/
 dist/