docs+ci: add PR packaging template + enforce it in CI

.github/PULL_REQUEST_TEMPLATE.md

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+## What I built
+- Implemented pipeline functions in `src/pipeline.py` (the three `NotImplementedError` stubs)
+- Pinned dependencies in `requirements.txt`
+- Cache-friendly `Dockerfile`
+- CI workflow in `.github/workflows/ci.yml`
+- ACR push (Task 7): image pushed to the class registry, screenshot committed
+- AI usage: `AI_ASSIST.md`
+
+## How to review
+- Code: read `src/pipeline.py` and `tests/test_pipeline.py`.
+- CI: see the green run on this PR, or the committed screenshot of the ACR push.
+- AI usage: `AI_ASSIST.md`.
+
+## How to run
+From a clean clone:
+
+```bash
+python -m venv .venv && source .venv/bin/activate
+pip install -r requirements.txt
+API_KEY=test pytest -q
+docker build -t my-pipeline:1.0 .
+docker run --rm -e API_KEY=test my-pipeline:1.0
+```
+
+Prerequisite: Docker installed. The `AZURE_CREDENTIALS` for Task 7 come from your teacher over Slack.
+
+## What reviewers should see (expected results)
+Fill in what your run actually produces, so a reviewer can eyeball correctness:
+- `pytest` result: <e.g. all tests pass, N passed>
+- Docker run output: <e.g. one line of pipeline output / row count>
+- ACR image tag pushed: <e.g. my-pipeline:1.0>
+
+## Known limitations / out of scope
+- <e.g. ACR push done manually rather than from CI; one edge case not handled>
+- Write "none" if everything in the assignment is done and working.
+
+## Extra completed
+- [ ] Any bonus / stretch items from the chapter
+
+## Self-check
+- [ ] `bash .hyf/test.sh` passes
+- [ ] `API_KEY=test pytest -q` passes locally
+- [ ] No credentials committed (no secrets in code, `.env`/creds are gitignored)
+- [ ] Screenshot of the ACR push is committed

.github/workflows/pr-body-check.yml

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+name: PR body check
+
+# Fails the check when a pull request description is missing the sections from
+# .github/PULL_REQUEST_TEMPLATE.md. GitHub only auto-fills that template in the
+# web "compose" form and in `gh pr create` with no --body; a PR opened through
+# the REST API or `gh pr create --body "..."` (the path most AI tools take)
+# silently skips it. This check is the only thing that actually enforces it.
+#
+# Recovery is automatic: editing the PR description fires the `edited` event and
+# re-runs this check with the new body. No new commit or manual re-run needed.
+
+on:
+  pull_request:
+    types: [opened, edited, reopened, synchronize]
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check required sections are present
+        env:
+          PR_BODY: ${{ github.event.pull_request.body }}
+        run: |
+          set -euo pipefail
+          required=(
+            "## What I built"
+            "## How to review"
+            "## How to run"
+            "## What reviewers should see"
+            "## Self-check"
+          )
+          missing=()
+          for section in "${required[@]}"; do
+            if ! printf '%s' "$PR_BODY" | grep -qiF "$section"; then
+              missing+=("$section")
+            fi
+          done
+          if [ ${#missing[@]} -ne 0 ]; then
+            echo "::error::Your PR description is missing required sections. Start from the template (.github/PULL_REQUEST_TEMPLATE.md) and keep these headings:"
+            for m in "${missing[@]}"; do echo "  - $m"; done
+            echo ""
+            echo "If you (or an AI tool) opened this PR without the template, click 'Edit' on the"
+            echo "PR description, paste the template, and fill it in. Editing the description"
+            echo "re-runs this check automatically. A complete PR is easy to review and"
+            echo "reproducible: that is part of the assignment."
+            exit 1
+          fi
+          echo "All required PR sections present."