Migrate inline Slack notifications to pg-actions reusable workflows (#1)

Replaces inline slackapi/slack-github-action steps with the centralised
slack-notify-start and slack-notify-end reusable workflows from pg-actions.
Restructures into 3-job pattern: slack-start → build → slack-end.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: pgmac

.github/workflows/docker-image.yml

@@ -5,65 +5,33 @@ on:
     tags:
       - "*.*.*"
   workflow_dispatch:
+
 jobs:
+  slack-start:
+    uses: pgmac-net/pg-actions/.github/workflows/slack-notify-start.yml@main
+    secrets: inherit
+
   build-n-push:
+    needs: [slack-start]
     runs-on: self-hosted
     steps:
-    - uses: actions/checkout@v3
-    - name: Set the image version
-      id: vars
-      run: echo "tag=${GITHUB_REF#refs/*/}" >> $GITHUB_OUTPUT
-    - name: Build the Docker image
-      run: docker build . --file Dockerfile --tag macro.int.pgmac.net:5000/gnutemps:${{ inputs.tags || steps.vars.outputs.tag }}
-    - name: Push to my internal registry
-      if: github.ref == 'refs/heads/"master"'
-      run: docker push macro.int.pgmac.net:5000/gnutemps:${{ inputs.tags || steps.vars.outputs.tag }}
-    - name: Exit code failure
-      if: failure()
-      run: |
-        echo "colour=danger" >> $GITHUB_ENV
-        echo "icon=🛑" >> $GITHUB_ENV
-    - name: Exit code cancelled
-      if: cancelled()
-      run: |
-        echo "colour=warning" >> $GITHUB_ENV
-        echo "icon=⚠" >> $GITHUB_ENV
-    - name: Exit code success
-      if: success()
-      run: |
-        echo "colour=good" >> $GITHUB_ENV
-        echo "icon=✅" >> $GITHUB_ENV
+      - uses: actions/checkout@v3
+      - name: Set the image version
+        id: vars
+        run: echo "tag=${GITHUB_REF#refs/*/}" >> $GITHUB_OUTPUT
+      - name: Build the Docker image
+        run: docker build . --file Dockerfile --tag macro.int.pgmac.net:5000/gnutemps:${{ inputs.tags || steps.vars.outputs.tag }}
+      - name: Push to my internal registry
+        if: github.ref == 'refs/heads/"master"'
+        run: docker push macro.int.pgmac.net:5000/gnutemps:${{ inputs.tags || steps.vars.outputs.tag }}
 
-    - name: Send Slack message
-      uses: slackapi/slack-github-action@v1.23.0
-      with:
-        payload: |
-          {
-            "channel": "builds",
-            "attachments": [
-              {
-                "mrkdwn_in": ["text", "pretext"],
-                "fallback": ${{ toJSON(join(github.event.commits.*.message, '<br>') || ':point_right: Manually triggered') }},
-                "color": "${{ env.colour || 'grey' }}",
-                "pretext": "${{ env.icon || '?' }} ${{ github.workflow }} (${{ github.ref_name }}) #${{ github.run_number }}",
-                "author_name": "${{ github.triggering_actor || github.actor }}",
-                "title": "${{ github.workflow }}",
-                "title_link": "${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}",
-                "text": ${{ toJSON(join(github.event.commits.*.message, '\n') || ':point_right: Manually triggered') }}
-              },
-              {
-                "blocks": [
-                  {
-                    "type": "section",
-                    "text": {
-                      "type": "mrkdwn",
-                      "text": "<${{ github.event.pull_request.html_url || github.event.head_commit.url || github.server_url }}|View commit>"
-                    }
-                  }
-                ]
-              }
-            ]
-          }
-      env:
-        SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
-        SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK
+  slack-end:
+    if: always()
+    needs: [slack-start, build-n-push]
+    uses: pgmac-net/pg-actions/.github/workflows/slack-notify-end.yml@main
+    with:
+      ts: ${{ needs.slack-start.outputs.ts }}
+      start: ${{ needs.slack-start.outputs.start }}
+      startfmt: ${{ needs.slack-start.outputs.startfmt }}
+      status: ${{ needs.build-n-push.result }}
+    secrets: inherit