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

[lassebenni]

What I built

Adds a package-complete PR template plus CI enforcement to this assignment repo.

• .github/PULL_REQUEST_TEMPLATE.md: tailored to this week's deliverables, with sections What I built / How to review / How to run / What reviewers should see (expected results) / Known limitations / Self-check. Gives a reviewing mentor a package-complete, reproducible submission.
• .github/workflows/pr-body-check.yml: fails a PR whose description is missing the required headings. GitHub only auto-injects the template in the web compose form / gh pr create without --body; a PR opened via the REST API or --body "..." (the path most AI tools take) skips it silently. This check closes that gap. Editing the PR description re-runs the check automatically (no new commit needed).

How to review

Two added files (one edited on Week 11). Read the template top-to-bottom; the workflow greps case-insensitively for 5 headings.

How to run

No runtime. Verified locally: the filled template passes the check; an empty/free-form body fails and lists the missing headings.

What reviewers should see (expected results)

• Filled template -> check passes (see this PR's own PR body check).
• Blob body -> check fails, lists missing sections.

Self-check

• Template + workflow validated locally against the check logic
• Workflow uses pull_request (not pull_request_target) with contents: read only
• No secrets introduced

🤖 Generated with Claude Code

[github-actions]

📝 HackYourFuture auto grade

Assignment Score: 39 / 100 ❌

Status: ❌ Not passed
Minimum score to pass: 60
🧪 The auto grade is experimental and still being improved

Test Details

=== Week 5 Autograder ===
  PASS: Level 1: required files (15/15 pts)
  FAIL: Dockerfile does not use python:3.11-slim base image
  FAIL: Dockerfile does not copy requirements before source code
  PASS: Dockerfile has a CMD instruction
  PASS: Level 2: Dockerfile (3/15 pts)
  PASS: tests/test_pipeline.py has 10 test functions (≥2 required)
  PASS: tests/test_pipeline.py has no NotImplementedError stubs remaining
  PASS: Level 3: unit tests (10/10 pts)
  FAIL: requirements.txt has no pinned packages (use package==version)
  PASS: Level 4: pinned dependencies (0/10 pts)
  PASS: ci.yml triggers on pull_request
  PASS: ci.yml triggers on push to main
  FAIL: ci.yml missing ruff check step
  FAIL: ci.yml missing ruff format step
  FAIL: ci.yml missing pytest step
  FAIL: ci.yml missing docker build step
  PASS: Level 5: CI workflow (8/20 pts)
  FAIL: pipeline.py does not read from os.environ or os.getenv
  FAIL: pipeline.py still contains NotImplementedError
  PASS: Level 6: env-var config (0/15 pts)
  FAIL: assets/acr_push_week5.png missing (Task 7 deliverable)
  PASS: Level 7: ACR screenshot (0/10 pts)
  PASS: AI_ASSIST.md has all three required sections
  FAIL: AI_ASSIST.md still contains TODO placeholders or is too short (681 chars)
  PASS: Level 8: AI report (3/5 pts)
  PASS: .gitignore correctly excludes __pycache__/, *.pyc, and .env

Score: 39 / 100  (passing: 60)  pass=false