fix: align scaffold env vars and links with Week 13 curriculum

[lassebenni]

Summary

• Rename DBRICKS_* → DATABRICKS_* in .env.example and profiles.yml.example so they match Ch4 / the assignment chapter.
• Fix Task 1 README link (week_13__6_assignment.md → week_13__7_assignment.md).
• Document --full-refresh baseline in Task 2 README; mention optional task-4/ in root README layout.
• Add PR body check enforcing the Week 13 PR template headings.

How to review

• Diff is small: env var rename, two README wording fixes, optional task-4/ line, and .github/workflows/pr-body-check.yml.
• Confirm Grade Assignment workflow is unchanged from the fork-safe pin already on main.

Secrets hygiene checklist

• No .env or profiles.yml files committed.
• No Databricks personal access tokens (dapi...) hardcoded.
• profiles.yml.example and .env.example templates present.

Test plan

• Confirm .env.example / profiles.yml.example use DATABRICKS_*
• Confirm Task 1 README opens week_13__7_assignment.md
• bash .hyf/test.sh still fails the empty scaffold (pass=false)
• PR body check + Grade Assignment both report on this PR after merge to main (body check runs from PR head)

[github-actions]

📝 HackYourFuture auto grade

Assignment Score: 10 / 100 ❌

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

Test Details

=== Databricks Lab Autograder ===
  ✗ FAIL  task-1: add pyspark_exploration.ipynb or .py
  ✗ FAIL  task-2/dbt_project.yml missing
  ✓ PASS  task-2/WRITEUP.md
  ✓ PASS  task-3/SCHEDULING.md
  ✓ PASS  AI_ASSIST.md
  ✓ PASS  Level 1: required files (0/15 pts)
  ✓ PASS  Level 2: PySpark notebook (0/25 pts)
  ✗ FAIL  models/marts/fct_trips.sql (or similar) not found
  ✗ FAIL  WRITEUP should explain is_incremental()
  ✗ FAIL  WRITEUP should reference {{ this }} or the incremental filter
  ✓ PASS  Level 3: dbt incremental + WRITEUP (0/30 pts)
  ✗ FAIL  task-3/screenshots/ should contain screenshots of Job config, green run, and paused schedule
  ⚠ WARN  SCHEDULING.md missing Databricks Job Run URL (paste URL from address bar)
  ✗ FAIL  SCHEDULING.md should explain when to use Databricks Jobs vs Airflow
  ✓ PASS  Level 4: Task 3 Job Scheduling (0/15 pts)
  ⚠ WARN  AI_ASSIST.md needs your documented prompt and rationale
  ✓ PASS  .gitignore excludes .env and profiles.yml
  ✓ PASS  profiles.yml.example present
  ✓ PASS  Level 5: AI_ASSIST & secrets hygiene (10/15 pts)

Score: 10 / 100  (passing: 60)  pass=false
Total: 10/100 — pass=false (passing threshold: 60)