Import-map-driven module resolution

Managed modules are stored as bare specifiers and loaded via import(), so resolution is delegated to the page's import map; absolute URLs are also accepted. Version switching is therefore a server-side import-map change (or a new URL), not a library API call. This keeps the library out of the business of rewriting paths and makes the page's module graph the single source of truth.

• Status: accepted
• Considered Options: (a) library-owned name→URL map (SPF's declare/path model) — rejected, duplicates what the import map already does and splits the module graph; (b) no names, raw specifiers only — rejected, loses the load-once/name-switching affordance; (c) import-map-driven — chosen.
• Consequences: pages using bare specifiers must ship an import map; the library must not cache module results across specifier resolutions (a name must be re-resolved on every load so import-map updates take effect).