Reintroduce multiple maps: per-map chunk directories + map_t name/mapSetMap

Move chunk assets from a single flat assetsraw/chunks (and assets/chunks)
into per-map assetsraw/maps/<map>/chunks (assets/maps/<map>/chunks), so
terrain mesh/model output no longer collides across maps sharing chunk
coordinates. map_t gains a name[MAP_NAME_MAX] field plus mapSetMap()/
mapIsLoaded() (checks name[0] == '\0') in place of the old bool loaded
flag; mapInit() now just resets state and mapSetMap() does the chunk
grid load. Updated the chunk asset tool and the map editor's dev
server/client to match.

test/rpg/entity/entitytestfixture.c

@@ -9,12 +9,13 @@
 #include "rpg/overworld/map.h"
 #include "rpg/overworld/tile.h"
 #include "util/memory.h"
+#include "util/string.h"
 
 void entityTestFixtureReset(void) {
   memoryZero(ENTITIES, sizeof(ENTITIES));
 
   memoryZero(&MAP, sizeof(map_t));
-  MAP.loaded = true;
+  stringCopy(MAP.name, "test", MAP_NAME_MAX);
   MAP.chunkPosition = (chunkpos_t){ 0, 0, 0 };
 
   chunk_t *chunk = &MAP.chunks[0];