Plugin endpoints collapse into one resource per plugin (tag 'plugins'): ops overwrite each other #202

NetBox tags every plugin endpoint with the single tag plugins. _resource_from_path (nsc/builder/build.py) anchors on the tag's path segment (plugins), so the "resource" becomes the plugin name (/api/plugins/<plugin>/<resource>/… → resource <plugin>). All of a plugin's endpoints then land in one resource, and _attach lets each CRUD slot be overwritten by whichever path comes last.

Seen on NetBox 4.7.3 + netbox-branching 1.2.2 (the e2e-branching stack). nsc plugins branching --help:

list      Get a list of change diff objects.   ← /changes/
get       Get a change diff object.            ← /changes/{id}/
create    Post a list of branch objects.       ← /branches/
update / replace / delete                      ← /branches/{id}/
branches-merge-create, branches-sync-create, …  (custom actions)

• branches list/get are unreachable, because changes overwrote them.
• branch-events and branchable-models don't appear at all.
• list and create under the same command act on different objects. With --apply, that's a correctness hazard.

Expected: nsc plugins <plugin> <resource> <verb> (or nsc <plugin> <resource> …), one resource per /api/plugins/<plugin>/<resource>/ path. The resource should be derived from the path, not anchored on the generic plugins tag.

Docs: docs/guides/working-with-plugins.md documents nsc my_plugin widgets list (assuming a per-plugin tag), which doesn't match what real NetBox schemas produce today.

This affects every plugin, not only Branching. Found while working on #180. Its optional e2e assertion against the real changes endpoint is blocked on this, because the endpoint currently surfaces as nsc plugins branching list.