Find a full install in host.factorio_directory instead of a setting

Per review, drop host.factorio_graphics_directory. findVersion takes a
headless option that filters installs by build, telling them apart by
data/base/graphics/icons. When the instance runs the headless build the
export looks for a full install of the same major.minor version in the
host's factorio directory. Server startup is unchanged.

If none is found the export still runs, and the reason is included in
the missing icons warning.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/configuration.md

@@ -354,20 +354,11 @@ Defaults to a random 31 bit number.
 
 Directory to look for the Factorio server(s) in.
 This can either point to a Factorio server directory, or to a directory containing multiple versions of the Factorio server.
+The headless build has no graphics, so when exporting data from an instance running it the base game's icons are read from a full install of the same major and minor version in this directory instead, if there is one.
 
 Defaults to "factorio".
 
 
-### host.factorio_graphics_directory
-
-Directory to read the base game's icons from when exporting data.
-The headless build of Factorio has no graphics, so instances running it export none of the base game's icons unless this points to a full install of Factorio.
-Like `host.factorio_directory` this can either point to a Factorio directory, or to a directory containing multiple versions, in which case the latest one matching the major and minor version of the instance is used.
-If there is no install matching the instance, a warning is logged and the data is exported without it.
-
-Defaults to null.
-
-
 ### host.mods_directory
 
 Directory the host stores mods downloaded from the controller in.