[dv] replace NLSR management naming with DV-specific endpoints #243

DV on main currently uses /localhost/nlsr for local management, including /localhost/nlsr/status and RIB readvertising commands.
This makes DV appear to depend on NLSR and confuses consumers.

It currently reuses NSLR namespace, which has nothing to do with the DV implementation.

This came up during review of #242. Handle the migration separately from the status dataset and page.

The change needs coordinated router and SDK updates. Renaming the router prefix alone disconnects the existing readvertising mechanism: ndnd put --expose still registers locally, but its prefix is no longer announced by DV.

Use the dv2 branch as a reference (not final):

• /localhost/dv/status for local status.
• /localhost/dv/prefix/announce and withdraw for local advertising.
• Signed /localhop/route/insert requests for remote clients.

Define the migration and compatibility behavior explicitly. Update the router, SDK, CLI tools, documentation, and tests together.
Verify local and browser/remote applications, including announcement, withdrawal, expiration/renewal, and authorization.

Keep this scoped to management naming and prefix advertising;
porting DV2's PET/PSD forwarding redesign is outside this issue.

Related: #69, #141, #242.