Configure submodules to track main branch and auto-update on build

- Add branch = main to submodules in .gitmodules
- Update build.sh to fetch latest from main before building
- Update hedit submodule to v0.6.2-alpha

Author: neuromechanist

.gitmodules

@@ -1,6 +1,8 @@
 [submodule "hedit"]
 	path = hedit
 	url = https://github.com/Annotation-Garden/hedit.git
+	branch = main
 [submodule "image-annotation"]
 	path = image-annotation
 	url = https://github.com/Annotation-Garden/image-annotation.git
+	branch = main

build.sh

@@ -6,6 +6,9 @@ set -e
 echo "Initializing submodules..."
 git submodule update --init --recursive
 
+echo "Updating submodules to latest from main branch..."
+git submodule update --remote --merge
+
 echo "Building documentation..."
 mkdocs build