Add optional `displayName` field to the plugin manifest

[aaronpowell]

Summary

The plugin manifest currently only has a name field, which doubles as both the machine identifier and the user-facing name. However, name is subject to strict constraints (§5.5): lowercase a-z0-9-. only, 1–64 chars, no leading/trailing hyphens or consecutive separators. This makes it unsuitable as a human-readable label in host UIs.

Proposal

Add an optional  displayName  string field to plugin.json that hosts MAY surface in user interfaces instead of `name.

• The displayName is optional; if present it MUST be a string.
• Hosts MAY use displayName in user interfaces instead of name.
• If absent, hosts MUST fall back to name as the display name.

This cleanly separates the constrained machine identifier (name) from an unconstrained, human-friendly label (displayName).

Example

{
  "$schema": "https://open-plugins.com/schemas/1.0.0/plugin.schema.json",
  "name": "plugin-name",
  "displayName": "Plugin Name",
  "version": "1.2.0"
}

Proposed changes

• Add displayName to the JSON schema (schemas/1.0.0/plugin.schema.json).
• Document displayName in the metadata field table (§5.4) and add a dedicated subsection (§5.7).
• Clarify §5.3 so name is described as the plugin identifier (see §5.5 constraints) rather than "human-readable", now that displayName fills the human-readable role.