New platform administration area

The update adds a new Administration area and stable /admin entry point for platform administrators. The area combines Users, Projects, Shared providers, and Notifications in one interface with local navigation. In Users, administrators can search records, create and edit users, enable or disable access, and reset passwords. A one-time temporary password appears once in a distinct dialog; after dismissal, Escape, or leaving the page it is removed from the DOM and is not restored by ordinary detail reads, while the server response uses no-store cache controls. In Projects, administrators can view projects, edit basic settings, manage members and roles, transfer ownership, and archive or restore projects. Shared providers allows configuration of shared processing connections and health diagnostics without exposing secrets. Project processing now shows the effective source used: PROJECT, SHARED, or UNAVAILABLE. Project HTTP notifications add a safe delivery history for that project only, including status, basic diagnostics, and retry for failed deliveries. The platform notification view shows cross-project operational metadata without package or source content. Regular users and service accounts do not see the Administration entry and receive a server-side denial when accessing /admin directly. The change also extends routing, template, static client, and authorization-boundary verification.