chore: migrate repository to Librarian (#1643)

* chore: migrate repository to Librarian

Towards googleapis/librarian#2417

* chore: comment/format only changes

- The source root doesn't need quoting
- Updated internal/version.go header format

* chore: remove vestigial repo-config.yaml

* chore: change changelog header

Author: jskeet

.github/release-please.yml

@@ -0,0 +1,8 @@
+# Hand-maintained configuration for libraries.
+#
+# All libraries with handwritten code (core, hybrid and handwritten)
+# libraries have "release_blocked: true" so that releases are
+# explicitly initiated
+libraries:
+  - id: "generator"
+    release_blocked: true

.librarian/config.yaml

@@ -0,0 +1,7 @@
+image: us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/librarian-go:latest
+libraries:
+  - id: generator
+    version: 0.53.1
+    source_roots:
+      - .
+    tag_format: 'v{version}'

.librarian/state.yaml

@@ -1,4 +1,4 @@
-# Changelog
+# Changes
 
 ## [0.53.1](https://github.com/googleapis/gapic-generator-go/compare/v0.53.0...v0.53.1) (2025-05-30)