(release) Prepare 1.0.0 release metadata

Add the initial 1.0.0 changelog, bump the package/application version,
and expose the release version through `pobsync --version`.

Cover the version output in the console entrypoint tests.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pobsync"
-version = "0.1.0"
+version = "1.0.0"
 description = "Pull-based rsync backup tool with hardlinked snapshots"
 requires-python = ">=3.11"
 dependencies = [