fix: validate time_range_minutes from CLI args in run.py

[Sanjays2402]

What

Fix inconsistent handling of time_range_minutes in sre_agent/run.py between the CLI-argument and environment-variable code paths. The CLI path now validates the value the same way the env path does.

Why

The documented invocation in DEVELOPMENT.md is:

uv run python run.py /aws/containerinsights/no-loafers-for-you/application cartservice

…optionally with a third positional argument for minutes. In _load_request_from_args_or_env (src/sre_agent/run.py:L26), the CLI branch calls int(sys.argv[3]) directly, while the env branch (L38-L46) already wraps the parse in try/except ValueError and rejects <= 0.

Two real issues follow:

1. Unhandled crash on typo. A non-integer third argument raises ValueError: invalid literal for int() with base 10: 'abc' with a full traceback instead of the friendly "time_range_minutes must be an integer." message the env path prints.
2. Silent acceptance of invalid values. python -m sre_agent.run foo bar 0 and ... -5 are accepted on the CLI path, even though the env path rejects both. The same-shape validation in src/sre_agent/cli/mode/remote/aws/ecs/steps.py:L402-L409 also rejects <= 0, so the CLI path is the outlier.

Reproduction (before this patch):

$ python -c "import sys; sys.argv=['run.py','logs','svc','abc']; \
    from sre_agent.run import _load_request_from_args_or_env; \
    _load_request_from_args_or_env()"
ValueError: invalid literal for int() with base 10: 'abc'

$ python -c "import sys; sys.argv=['run.py','logs','svc','-5']; \
    from sre_agent.run import _load_request_from_args_or_env; \
    print(_load_request_from_args_or_env())"
('logs', 'svc', -5)   # silently accepted, feeds a negative timedelta into CloudWatch

How

• Extract the parse-and-validate logic into _parse_time_range_minutes(raw: str) -> int and call it from both the CLI-args branch and the env branch.
• Error messages now use the generic label time_range_minutes so they read naturally for both sys.argv[3] and TIME_RANGE_MINUTES.
• No change to valid-input behaviour: int(raw) with raw > 0 returns the same value as before.

Extra

No new dependencies.

Checklist

• I have run application tests ensuring nothing has broken.
• I have updated the documentation if required. (No user-visible docs change; error strings only.)
• I have added tests which cover my changes.

Testing

• Added tests/test_run_args.py covering: valid input, non-integer input, zero, negatives, and a round-trip through _load_request_from_args_or_env for both failure modes and the happy path.
• Local run (uv run pytest tests/): 8 passed (1 pre-existing + 7 new).
• ruff check --config=ruff.toml and ruff format --config=ruff.toml --check: clean.
• uv run mypy --config-file=mypy.ini $(find src/sre_agent -name '*.py'): Success: no issues found in 94 source files.

Type of change

Bug fix.