Adds docs/rewrite/DEVIANT_FIXES.md, the single list of places where the
Rust port deliberately behaves differently from Ghostty 1.3.1:
- 30 upstream bugs fixed instead of replicated (memory safety/UB,
infinite loops, crashes, data loss), each with Zig file:line, both
behaviours, the commit that introduced the Rust behaviour and its test
(a few Zig locations are marked unverified);
- 11 upstream quirks deliberately kept as in Zig;
- 18 other deliberate deviations (out-of-scope Swift app, platforms that
are only compile-checked, library substitutions with observable
differences).
Deviations made from now on are committed alone as fix-deviant(<scope>)
and added here; earlier ones are bundled in larger commits, which is why
the register records their hashes.
