fix: DjangoInstrumentor poisons settings when OTEL_EXPORTER_OTLP_ENDPOINT is set

[khvn26]

Closes #191.

In this PR, we reorder ensure_cli_env() so that sys.path.append(os.getcwd()) and os.environ.setdefault("DJANGO_SETTINGS_MODULE", ...) run before the OTel setup block. Previously, DjangoInstrumentor().instrument() accessed settings.MIDDLEWARE before the project directory was on sys.path, causing Django to fail the settings import. The instrumentor silently caught the error and called settings.configure() with empty defaults, poisoning Django for the rest of the process — making commands like flagsmith docgen disappear.

Also, we migrate test_main.py from unittest.mock.patch/patch.dict to pytest-mock/monkeypatch.setenv, and add tests for the docgen and task-processor argv branches.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.95%. Comparing base (396f138) to head (a0e4e1c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #192      +/-   ##
==========================================
+ Coverage   96.88%   96.95%   +0.06%     
==========================================
  Files         101      101              
  Lines        3983     4008      +25     
==========================================
+ Hits         3859     3886      +27     
+ Misses        124      122       -2     

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[khvn26]

Tested on Depot CI (where OTEL_EXPORTER_OTLP_ENDPOINT is set as a platform default). With the fix installed from this branch, flagsmith help shows the full command list including common.core commands. Without the fix, only [django] commands appear because DjangoInstrumentor poisons settings before CWD is on sys.path.