Plugin system should support a displayName field for human-readable names

Feature Request

Add displayName support to the plugin manifest schema (plugin.json and marketplace entries).

Problem

The plugin UI currently auto-formats the name field (kebab-case → sentence case), which produces incorrect results for names with non-standard casing or capitalization conventions. There is no way to override this behavior.

Proposed Fix

Honor a displayName field in plugin.json and marketplace.json entries when present, falling back to auto-formatting name if absent. This is a standard pattern in other plugin ecosystems (VS Code extensions, npm packages, etc.).

Example:

{
  "name": "my-plugin",
  "displayName": "My Plugin",
  ...
}

Impact

Without this, plugin authors have no way to control how their plugin names appear in the UI, which is especially problematic for names with acronyms, brand names, or specific capitalization requirements.