Build 4 (5b4c9c4)

fix: vendor the patched sourcenet Lua and degrade without it

A clone of this repository was not installable on its own: the addon
includes sourcenet/incoming.lua, which only ever reached a server through
the release archive that CI assembled. Installing from the repository left
the include failing and then FilterIncomingMessage nil, taking the whole
console filter down with it.

The patched Lua half is now vendored under addon/lua/sourcenet, so the
addon directory is complete as it stands, and CI fails the build if it
drifts from the pinned upstream with the patch applied. The upstream copy
is no longer packed on top of it.

The include is also guarded now: without the sourcenet Lua the command
filter reports itself unavailable and stops, which is what the rest of the
addon already did for its own missing pieces.