Rename framework/ to diachron/ and update all references

Update paths in .gitignore, cmd, develop, mgmt, sync.sh, check.sh,
fixup.sh, CLAUDE.md, docs/new-project.md, and backend/*.sh scripts.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

develop

@@ -13,7 +13,7 @@ if [ $# -lt 1 ]; then
     echo "Usage: ./develop <command> [args...]"
     echo ""
     echo "Available commands:"
-    for cmd in "$DIR"/framework/develop.d/*; do
+    for cmd in "$DIR"/diachron/develop.d/*; do
         if [ -x "$cmd" ]; then
             basename "$cmd"
         fi
@@ -24,4 +24,4 @@ fi
 subcmd="$1"
 shift
 
-exec "$DIR"/framework/develop.d/"$subcmd" "$@"
+exec "$DIR"/diachron/develop.d/"$subcmd" "$@"