Refactor logger with defensive improvements and reduced complexity

[z80020100]

Summary

• Replace UtcOffset::current_local_offset().unwrap() with unwrap_or(UtcOffset::UTC) to prevent panic in multi-threaded environments
• Replace deeply nested generic type aliases (FIXME: clippy::type_complexity) with Box<dyn LevelFilterReloader> trait object
• Refactor reconfig() to parse-then-apply pattern with rollback on partial failure
• Extract parse_level_filter() helper to reduce duplication
• Lower default log levels to TRACE and adjust init/config log levels

Closes #36
Closes #38

Test plan

• cargo build passes
• cargo fmt --all -- --check passes
• cargo clippy passes with no warnings
• cargo test passes