docs(i18n): update bg README to match ja/en structure (#281)

- Restructure Quick Start from 4 steps to 3 steps (UI-based setup)
- Add Profile Management section with UI guidance
- Add Delete Identity command to Commands table
- Reorder features list (Profile Management UI first)
- Update image paths from ja/ to bg/
- Keep Bulgarian sample profile name (Саша Иванов)
- Align terminology with l10n bundle (профил)

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Model-Raw: claude-opus-4-5-20251101

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: nullvariant