fix: ignore constant-return CLI main

[ApexWorm]

Problem

The constant-return detector flags ordinary CLI main entry points that return zero on every successful path, even when the function is invoked only through an exact module entrypoint guard. This produces a false positive for deployment scripts.

Fix

Recognize a top-level main invoked by an exact name module guard and exempt only that function from constant-return detection. Unguarded main functions, non-main guarded functions, and nested main functions remain detected.

Verification

• 41 AST smell tests passed
• 284 Python-language tests passed
• The patched detector no longer flags the real deployment renderer main; the current detector does
• Diff whitespace check passed
• Ruff has the same pre-existing UP038 finding on base and branch