MidnightNameplates 0.9.1 - Phase 9.1 Visual Rule Manager

Added:
- Visual Rules manager under /mnp -> Rules.
- NPC Rules / Spell Rules switch.
- Search/filter box.
- Add, select, duplicate and delete rules.
- Rename selected rule.
- Enable/disable rule.
- Priority: LOW / NORMAL / HIGH / CRITICAL.
- NPC editor: scale, alpha, health-color override toggle, frame-color override toggle.
- Spell editor: cast-color override toggle, cast-border override toggle, emphasize toggle.
- Existing Phase 9 runtime rule engine remains intact and WoW 12.1 secret-safe.

Next Phase 9.2:
- Full rule color pickers.
- Better paged/scrollable rule list.
- Live rule preview.
- Richer priority presentation and matching options.
