Add basic Environment Templates administration to Core Web

[SaladDay]

Administrators currently have to open Session creation to find basic Environment Templates. Add a dedicated Templates view for the existing public client operations: complete catalog reads, name/network creation and partial updates, and confirmed deletion. Successful changes refresh the catalog shared with Session creation.

The view distinguishes empty, unsupported and failed reads; it fences responses after Core changes and never automatically replays an uncertain write. It does not create Sessions, allocate Runtime instances or call models. Advanced Template profiles remain explicitly outside the current client coverage. No server APIs, queries, runtime behavior, installer or business features change.

Validation: targeted component/client/type checks and Web build; 15 new Chrome browser scenarios; real Core with dedicated PostgreSQL and two project identities covering CRUD, pagination, omitted-field preservation, unauthenticated rejection and cross-project read/update/delete denial. Independent GPT-6 Astra high review passed, including 17 focused unit tests and 15 browser cases. Server make check passed its database/sqlc/Go/Core/microsandbox/Claude gates but cannot launch browser tests because the host lacks libatk-1.0.so.0 (including with its installed Chromium). Full make check-web passed on desktop Chrome: 903 client/Web unit tests and all 94 browser cases. Remaining MiniMax/Rust gates passed on the server (including format and Clippy). No repository test configuration changes are included. All component gates, real API acceptance and independent review have passed; this does not claim a clean single-host make check run.