Audit project against Rust best practices

[ErickJ3]

Audit of the workspace against Apollo's Rust best practices handbook plus targeted fixes for the issues found. Covers panic removal in production paths (ui.rs, storage Mutex locks, CLI path handling), a real bug where format!("{:?}", enum) was persisted to SQLite but parse_severity_level only matched 6 of 25 SeverityLevel variants, batched storage inserts under a single transaction, hex encoding via lookup table, removal of redundant clones, inheritance of the workspace [lints] block (previously dead config), and module/crate documentation.

Clippy warnings drop from 743 to 584, all 126 tests pass, release build clean.

Verified:

• cargo fmt --all --check
• cargo clippy --workspace --all-targets --locked
• cargo test --workspace --locked
• cargo build --workspace --release --locked