Add label selection action

.github/workflows/label-by-group.yml

@@ -0,0 +1,52 @@
+name: Label PR by group
+
+on:
+  pull_request_target:
+    types: [opened, edited, reopened]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  label-selection:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set label from PR title
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const title = context.payload.pull_request.title;
+
+            // Expected title format: "<hw number>. <full name>. <group number>"
+            const parts = title.split(".").map((part) => part.trim());
+
+            if (parts.length !== 3 || parts.some((part) => part.length === 0)) {
+              console.log(`Title "${title}" does not match the expected template, skipping.`);
+              return;
+            }
+
+            const [hwNumber, , groupNumber] = parts;
+
+            if (!/^\d+$/.test(hwNumber)) {
+              console.log(`Title "${title}" does not match the expected template, skipping.`);
+              return;
+            }
+
+            const { data: labels } = await github.rest.issues.listLabelsForRepo({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+            });
+
+            const matchingLabel = labels.find((label) => label.name === groupNumber);
+
+            if (!matchingLabel) {
+              console.log(`No label named "${groupNumber}" found, skipping.`);
+              return;
+            }
+
+            await github.rest.issues.addLabels({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.payload.pull_request.number,
+              labels: [matchingLabel.name],
+            });