fix(manifest): apply per-package snapshot-label from config

`extractReleaserConfig` was not mapping the `snapshot-label` key from
per-package `release-please-config.json` blocks, and `mergeReleaserConfig`
was not propagating it from the root default into per-package configs.
As a result, Java/Maven snapshot PRs fell back to `DEFAULT_SNAPSHOT_LABELS`
(`['autorelease: snapshot']`) regardless of configuration.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: LudovicTOURMAN

src/manifest.ts

@@ -1422,6 +1422,7 @@ function extractReleaserConfig(
     labels: config['label']?.split(','),
     releaseLabels: config['release-label']?.split(','),
     extraLabels: config['extra-label']?.split(','),
+    snapshotLabels: config['snapshot-label']?.split(','),
     skipSnapshot: config['skip-snapshot'],
     initialVersion: config['initial-version'],
     excludePaths: config['exclude-paths'],
@@ -1790,6 +1791,7 @@ function mergeReleaserConfig(
     skipSnapshot: pathConfig.skipSnapshot ?? defaultConfig.skipSnapshot,
     initialVersion: pathConfig.initialVersion ?? defaultConfig.initialVersion,
     extraLabels: pathConfig.extraLabels ?? defaultConfig.extraLabels,
+    snapshotLabels: pathConfig.snapshotLabels ?? defaultConfig.snapshotLabels,
     excludePaths: pathConfig.excludePaths ?? defaultConfig.excludePaths,
     dateFormat: pathConfig.dateFormat ?? defaultConfig.dateFormat,
   };

test/fixtures/manifest/config/snapshot-labels.json

@@ -0,0 +1,13 @@
+{
+  "release-type": "java",
+  "snapshot-label": "global-snapshot",
+  "packages": {
+    ".": {
+      "component": "root"
+    },
+    "node-lib": {
+      "component": "node-lib",
+      "snapshot-label": "per-package-snapshot"
+    }
+  }
+}

test/manifest.ts

@@ -506,6 +506,38 @@ describe('Manifest', () => {
         'lang: nodejs',
       ]);
     });
+    it('should read snapshot labels from manifest', async () => {
+      const getFileContentsStub = sandbox.stub(
+        github,
+        'getFileContentsOnBranch'
+      );
+      getFileContentsStub
+        .withArgs('release-please-config.json', 'main')
+        .resolves(
+          buildGitHubFileContent(
+            fixturesPath,
+            'manifest/config/snapshot-labels.json'
+          )
+        )
+        .withArgs('.release-please-manifest.json', 'main')
+        .resolves(
+          buildGitHubFileContent(
+            fixturesPath,
+            'manifest/versions/versions.json'
+          )
+        );
+      const manifest = await Manifest.fromManifest(
+        github,
+        github.repository.defaultBranch
+      );
+      expect(manifest['snapshotLabels']).to.deep.equal(['global-snapshot']);
+      expect(manifest.repositoryConfig['.'].snapshotLabels).to.deep.equal([
+        'global-snapshot',
+      ]);
+      expect(
+        manifest.repositoryConfig['node-lib'].snapshotLabels
+      ).to.deep.equal(['per-package-snapshot']);
+    });
     it('should read exclude paths from manifest', async () => {
       const getFileContentsStub = sandbox.stub(
         github,