docs: add smell files (anti-patterns + common mistakes)
anti-patterns.md: 10 entries, 490 lines — what the stdlib avoids
common-mistakes.md: 10 entries, 508 lines — language transition smells
Covers: unwrap in library code, String errors, unsafe without SAFETY,
clone as borrow-checker escape, Deref as inheritance, panic for
recoverable errors, god structs, Box<dyn Any>, static mut, stringly-typed APIs,
Arc<Mutex> everywhere, collect then iterate, index loops, try/catch
mentality, null sentinels, OOP hierarchies, global state, impl vs dyn.
Rodin
f270fc68c1