fix: use context manager for file reads in code_projects_api.py

[nwalio]

Background

In backend/app/modules/code/code_projects_api.py, two file reads use the pattern json.loads(open(path, encoding="utf-8").read()), which opens a file handle without explicitly closing it. The handle is eventually collected by the garbage collector, but if json.loads raises before the handle is released, it leaks. Under PyPy or high-concurrency workloads, these accumulate.

Changes

Replaced both occurrences with the with open(...) as f: context manager pattern:

• Line 1299 (get_pipeline_results): reading pipeline_results.json
• Line 1374 (auto_fix_pipeline): reading previous pipeline results

Each change adds one line (the with statement) and re-indents the json.loads call inside the block. No behavioral change — the same data is read and parsed.

Before/After

# Before
data = json.loads(open(results_path, encoding="utf-8").read())

# After
with open(results_path, encoding="utf-8") as _f:
    data = json.loads(_f.read())

Notes

The existing encoding="utf-8" parameter is preserved — this was already correct. The only change is ensuring the file handle is deterministically closed via the context manager protocol rather than relying on GC timing.

Verification

• py_compile confirms valid Python syntax
• New test tests/test_pr_06_code_projects_files.py runs two assertions:
  1. No open(...).read() patterns remain in the module
  2. At least 3 context-managed results_path opens exist (2 reads + 1 write)
• Both tests pass in the sandbox container