Fix/bugfixes and code quality

[harkaranbrar7]

Summary

Fixes 6 critical bugs and applies comprehensive code quality improvements following Rust best practices.

Bug Fixes

• files command ignoring CLI paths — was always scanning cwd regardless of user input
• CStyleClassifier misclassifying inline /* */ comments — lines like int x = 1; /* comment */ were counted as Comment instead of Pure
• PythonClassifier misclassifying triple-quotes with trailing code — """docstring""" x = 1 was counted as Docstring
• CI+JSON mode breaking parsers — summary line appended after JSON output
• JSON serialization errors silently swallowed — if let Ok(json) dropped failures
• Threshold aggregation missing fields — only summed 6 of 12 LangStats fields, skewing noise ratio

Code Quality

• Replace std::process::exit() with Result<ExitCode> pattern
• Extract aggregate_stats() to eliminate duplicate aggregation logic
• Apply all clippy fixes: uninlined format args, #[must_use], const fn, wildcard imports, cast safety, let-else patterns
• Add Rust, YAML, TOML language detection; Dockerfile/Makefile → Shell

Validation

• 5/5 tests pass
• cargo clippy — zero warnings
• cargo fmt — clean
• Verified against real git diffs and file scans