Host-neutral Emacs editor capability.

The returned map is data plus functions. A host-specific adapter may wrap it
in its own editor protocol; hive-emacs never imports or resolves that host.

IEditorPort reification over the addon's verb handlers.

The port is the hive-spi contract face of hive-emacs.tools.emacs: same
params maps in, same MCP response maps out. Registered as the :default
editor port when the addon initializes; consumers resolve it through
hive-spi.editor.registry, never through this ns.

Surfaces implemented: substrate, buffer, docs. IEditorDaemonPort is
deliberately absent — hive-emacs' daemon layer has no verb handlers yet, so
the adapter reports the surface as unsupported rather than reifying methods
that would throw.