Add dynamic OOUI namespace management interface

[Copilot]

Special:ManageNamespaces only offered a raw JSON textarea. This adds an OOUI interface that renders namespace definitions from the stored JSON and supports creating, renaming, deleting, and configuring namespaces.

Changes

• modules/ext.namespaceManager.js — Renders one panel per namespace with a field per JSON property, chosen by value type: boolean → toggle, number → number input, array → tag multiselect, string → text input. Add/Delete buttons manage namespaces; renaming edits the name field. Allocates the lowest free even id in 3000–4998 and warns when exhausted. Serializes every edit back into the raw field on change.
• includes/SpecialManageNamespaces.php — Loads the module, exposes current definitions via the wgNamespaceManagerData config var, adds the #namespacemanager-app mount point, and keeps the raw <textarea> as the submitted field (now hidden behind a toggle, and the no-JS fallback). Existing save/validation path is untouched.
• extension.json — Registers the ext.namespaceManager ResourceLoader module.
• modules/ext.namespaceManager.css — Panel/action styling; hides the raw field when JS is active.

Notes

• The raw JSON field remains the single submitted source of truth, so the server-side save flow is unchanged.
• Fields render from whatever properties exist on each object, so non-standard keys still surface.
• UI strings are hardcoded English, consistent with the existing special page.