Universal Spell Check v0.3.1

fix: prevent replacements from cascading onto their own output

"Burton Morgan Comp" was a case-sensitive prefix of its own canonical
"Burton Morgan Competition", causing it to fire on already-correct text
and produce "Competitionetition". Two fixes:

1. Remove "Burton Morgan Comp" from variants — it was the unsafe entry.
2. Rewrite ApplyReplacements to use a left-to-right positional scan that
   advances past the consumed variant, making cascading fires impossible.
3. Add load-time validation that detects and skips any variant that is a
   substring of its own canonical, logging replacements_variant_unsafe.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>