fix(tooling): treat an empty-string dep name as invalid, not a blank dep

split_dep_names' string branch returned { "" } for an empty string while the
table branch routes "" to `invalid` — the "ONE validity definition" the
docstring promises was inconsistent, and a caller passing "" would surface a
blank, label-less dep downstream. Route "" to `invalid` in the string branch
too, matching the table branch.

Author: charliie-dev

lua/modules/utils/tools.lua

@@ -33,6 +33,12 @@ M.SWEEP_DELAY_MS = 120000
 ---@return any[] invalid @Raw non-nil dropped entries, in order.
 local function split_dep_names(names)
 	if type(names) == "string" then
+		-- An empty string is invalid, same as in the table branch below — route
+		-- it to `invalid` so the ONE validity definition holds for both shapes
+		-- (a blank string must never read as a valid, label-less dep).
+		if names == "" then
+			return {}, { "" }
+		end
 		return { names }, {}
 	end
 	if type(names) ~= "table" then