fix(grading): stop autograder from silently crashing under bash 5

[lassebenni]

Summary

• ((var += expr)) reports a failing exit status whenever the resulting arithmetic value is 0 -- a well-known bash gotcha. Combined with set -euo pipefail, the grader silently dies mid-run the moment a student's running score hits exactly 0 at a checkpoint (e.g. a mostly-empty early submission).
• This only shows up on GitHub Actions' Ubuntu runners (bash 5+); it's invisible when testing locally on macOS (bash 3.2 ships without this strictness), which is how it went unnoticed.
• Also guards bare check_*() helper calls (which legitimately return 1 to signal warn/fail, not a script error) with || true so they don't trip set -e either.

Test plan

• bash -n .hyf/test.sh
• Reproduced against an empty scaffold repo with GNU bash 5: exit code 1 before the fix, exit code 0 after.
• Re-ran against a known-good local solution: score/pass output unchanged (regression-free).
• Confirm a real PR run in CI now completes the "Run tests" step for a low/zero-scoring submission.

🤖 Generated with Claude Code

[github-actions]

📝 HackYourFuture auto grade

Assignment Score: 18 / 100 ❌

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

Test Details

=== Week 6 Autograder ===
  ✓ PASS  found Dockerfile
  ✓ PASS  found requirements.txt
  ✓ PASS  found src/pipeline.py
  ✓ PASS  found AI_ASSIST.md
  ✓ PASS  found README.md
  ✓ PASS  found docs/ directory
  ✓ PASS  Level 1: required files (10/10 pts)
  ✗ FAIL  requirements.txt does not pin azure-storage-blob (expected line like 'azure-storage-blob==12.x.y')
  ✗ FAIL  requirements.txt does not pin psycopg2-binary (expected line like 'psycopg2-binary==2.x.y')
  ✓ PASS  Level 2: pinned dependencies (0/10 pts)
  ✓ PASS  Dockerfile uses a python:3.11 base image
  ✗ FAIL  Dockerfile does not copy requirements.txt before src/ (cache-unfriendly)
  ✗ FAIL  Dockerfile CMD is still the placeholder — replace it with the pipeline entry point
  ✓ PASS  Level 3: Dockerfile (3/10 pts)
  ✓ PASS  pipeline.py reads POSTGRES_URL and AZURE_STORAGE_CONNECTION_STRING from env
  ✗ FAIL  pipeline.py does not use 'from contextlib import closing' + 'with closing(...)' (Chapter 4 pattern)
  ✗ FAIL  pipeline.py does not silence the azure SDK logger (logging.getLogger("azure").setLevel(...))
  ⚠ WARN  pipeline.py still contains 'raise NotImplementedError' — finish the stubs before submitting
  ✓ PASS  Level 4: pipeline shape (5/15 pts)
  ✗ FAIL  pipeline.py does not use ON CONFLICT ... DO UPDATE (idempotent upsert)
  ✗ FAIL  pipeline.py does not use %s placeholders for parameterised SQL
  ✓ PASS  Level 5: idempotent upsert (0/15 pts)
  ✗ FAIL  no mention of sslmode=require in the repo — Azure Postgres rejects connections without it
  ✗ FAIL  pipeline.py does not use the azure-storage-blob SDK (BlobServiceClient)
  ✓ PASS  Level 6: connection + SDK (0/10 pts)
  ✗ FAIL  AI_ASSIST.md has section headers but is not filled in (665 chars, 3 TODO line(s); target 1800+ chars, 0 TODOs)
  ✓ PASS  Level 7: AI report (0/10 pts)
  ✗ FAIL  README.md is missing the '## Verification' heading (Task 5)
  ✓ PASS  Level 8: README verification (0/10 pts)
  ✗ FAIL  docs/execution_history.png not found (Task 5 deliverable)
  ✓ PASS  Level 9: execution screenshot (0/10 pts)
  ✓ PASS  .gitignore correctly excludes __pycache__/, *.pyc, and .env

Score: 18 / 100  (passing: 60)  pass=false