chore: add workflow to retarget main PRs to dev automatically

.github/workflows/auto-retarget-main-pr-to-dev.yml

@@ -0,0 +1,73 @@
+name: auto-retarget-main-pr-to-dev
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - reopened
+      - edited
+    branches:
+      - main
+
+permissions:
+  contents: read
+  issues: write
+  pull-requests: write
+
+jobs:
+  retarget:
+    if: github.actor != 'github-actions[bot]'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Retarget PR base to dev
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const pr = context.payload.pull_request;
+            const prNumber = pr.number;
+            const { owner, repo } = context.repo;
+
+            const baseRef = pr.base?.ref;
+            const headRef = pr.head?.ref;
+            const desiredBase = "dev";
+
+            if (baseRef !== "main") {
+              core.info(`PR #${prNumber} base is ${baseRef}; nothing to do.`);
+              return;
+            }
+
+            if (headRef === desiredBase) {
+              core.info(`PR #${prNumber} is ${desiredBase} -> main; skipping retarget.`);
+              return;
+            }
+
+            core.info(`Retargeting PR #${prNumber} base from ${baseRef} to ${desiredBase}.`);
+
+            try {
+              await github.rest.pulls.update({
+                owner,
+                repo,
+                pull_number: prNumber,
+                base: desiredBase,
+              });
+            } catch (error) {
+              core.setFailed(`Failed to retarget PR #${prNumber} to ${desiredBase}: ${error.message}`);
+              return;
+            }
+
+            const body = [
+              `This pull request targeted \`${baseRef}\`.`,
+              "",
+              `The base branch has been automatically changed to \`${desiredBase}\`.`,
+            ].join("\n");
+
+            try {
+              await github.rest.issues.createComment({
+                owner,
+                repo,
+                issue_number: prNumber,
+                body,
+              });
+            } catch (error) {
+              core.warning(`Failed to comment on PR #${prNumber}: ${error.message}`);
+            }