docs(spec): Restructure UX docs and add visual reference

Break up v2_ux.md (1400+ lines) into smaller, focused documents:
- v2_ux.md - Core UX (overview, server list, modals)
- v2_ux_features.md - Feature screens (Tools, Resources, etc.)
- v2_ux_handlers.md - Client handlers, form generation, errors
- v2_screenshots.md - Visual reference with Shadcn prototype screenshots

Add screenshots from Shadcn prototype to specification/screenshots/.
Update navigation headers across all spec files.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: olaservo

specification/README.md

@@ -1,6 +1,7 @@
 # Inspector V2 Brief 
 
-### Brief | [V1 Problems](v1_problems.md) | [V2 Scope](v2_scope.md) | [V2 Tech Stack](v2_tech_stack.md) | [V2 UX](v2_ux.md)
+### Brief | [V1 Problems](v1_problems.md) | [V2 Scope](v2_scope.md) | [V2 Tech Stack](v2_tech_stack.md)
+### UX: [Overview](v2_ux.md) | [Features](v2_ux_features.md) | [Handlers](v2_ux_handlers.md) | [Screenshots](v2_screenshots.md)
 
 ## Table of Contents
   * [Motivation and Context](#motivation-and-context)