Introduce ParseRuleKind.mixedMerchant to flag merchants whose category
varies (Ozon, marketplaces). When set, the pipeline suppresses the
merchant→category rule suggestion in the Inbox so the card shows
"confirm once" instead of "Create rule". Inbox action "Categories vary"
creates the marker rule, removes any existing merchant→category rule and
observed candidate, and rewrites the draft cache without the suggestion.
Adds findMixedMerchantRule lookup, InboxController.markMerchantMixed,
localizations (en/ru), UI in inbox_card/rule_editor, and tests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>