Repair embedded dependency build and test setup

Isolate vendored test registration, namespace project error codes, and update dependency revisions. Fix mutable sprite path handling, out-of-tree fixtures, and charviewer initialization while documenting the outstanding character-to-sprite refcount bug.

Co-authored-by: Codex (GPT-5) <noreply@openai.com>

.gitmodules

@@ -15,10 +15,10 @@
 	url = git@github.com:libsdl-org/SDL_ttf.git
 [submodule "deps/libsdlerror"]
 	path = deps/libakerror
-	url = https://source.home.aklabs.net/andrew/libsdlerror.git
+	url = https://source.starfort.tech/andrew/libakerror.git
 [submodule "deps/libakstdlib"]
 	path = deps/libakstdlib
-	url = https://source.home.aklabs.net/andrew/libakstdlib.git
+	url = https://source.starfort.tech/andrew/libakstdlib.git
 [submodule "deps/jansson"]
 	path = deps/jansson
 	url = git@github.com:akheron/jansson.git