fix: post-contest tech debt refactoring (closes #36)

[xodapi]

What was done

1. API key no longer stored plaintext in redb cache - cache key now uses hashed api_key via DefaultHasher
2. Race condition in daily.toml fixed - atomic write via temp file + rename, plus file locking via fs3
3. Thread spam in GUI fixed - generation counter prevents stale refresh results from overwriting fresh data
4. God-object refactoring - split monolithic lib.rs (~1250 lines) into:
   • �pi.rs - HttpClient, Router, network layer
   • parse.rs - data parsing, summarizing, demo payload
   • lib.rs - types, constants, formatting, config

How to verify

cargo test --locked cargo clippy --all-targets -- -D warnings cargo fmt --check

Closes

Closes #36