Add maiko, notecards, loops, test as git submodules

Removes maiko/ from .gitignore so it can be tracked as a submodule.
Each submodule is pinned to the current HEAD of its default branch
(master for maiko/test, main for notecards/loops).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitmodules

@@ -0,0 +1,16 @@
+[submodule "maiko"]
+	path = maiko
+	url = https://github.com/Interlisp/maiko
+	branch = master
+[submodule "notecards"]
+	path = notecards
+	url = https://github.com/Interlisp/notecards
+	branch = main
+[submodule "loops"]
+	path = loops
+	url = https://github.com/Interlisp/loops
+	branch = main
+[submodule "test"]
+	path = test
+	url = https://github.com/Interlisp/test
+	branch = master