chore: update Go module path to github.com/metamorphosis-dev/kafka

Module path now matches the GitHub mirror location.
All internal imports updated across 35+ files.

.forgejo/workflows/mirror.yml

@@ -0,0 +1,23 @@
+name: Mirror to GitHub
+
+on:
+  push:
+    branches: [main]
+    tags: ['v*']
+
+jobs:
+  mirror:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: https://github.com/actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Push to GitHub mirror
+        uses: https://github.com/ad-m/github-push-action@master
+        with:
+          github_token: ${{ secrets.GH_MIRROR_TOKEN }}
+          repository: metamorphosis-dev/gosearch
+          branch: ${{ github.ref_name }}
+          force: true