Migrate Dagger module to repo root with native container builds

Move the Dagger module from .dagger/ to the repo root (src/blumeops/),
rename from blumeops-ci to blumeops, and introduce native Dagger pipelines
that replace docker_build() for container builds.

docker_build() swallowed build errors — native pipelines surface full
output per step. Navidrome is the first container migrated as a proof of
concept (containers/navidrome/container.py).

- Containers with container.py use native Dagger builds
- Containers with only Dockerfile fall back to docker_build()
- dagger call container-version extracts VERSION from container.py
- CI workflow, container-list, container-version-check, and
  container-build-and-release all updated for hybrid mode

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,12 @@
+[project]
+name = "blumeops"
+version = "0.1.0"
+requires-python = ">=3.13"
+dependencies = ["dagger-io"]
+
+[build-system]
+requires = ["uv_build>=0.8.4,<0.9.0"]
+build-backend = "uv_build"
+
+[tool.uv.sources]
+dagger-io = { path = "sdk", editable = true }