fix: accept case-insensitive boolean flags

[hiSandog]

Summary

• parse optional boolean flag values case-insensitively
• remove case-insensitive true/false values from cleaned command args
• add unit coverage for uppercase boolean flag values

Validation

• git diff --check
• attempted: cargo test --manifest-path cli/Cargo.toml flags::tests::test_bool_flag_values_are_case_insensitive flags::tests::test_clean_args_removes_case_insensitive_bool_flag_values (cargo is not installed in this environment)

[vercel]

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