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>

check.sh

@@ -10,7 +10,7 @@ cd "$DIR"
 #
 exclusions="SC2002"
 
-source "$DIR/framework/versions"
+source "$DIR/diachron/versions"
 
 if [[ $# -ne 0 ]]; then
     shellcheck --exclude="$exclusions" "$@"
@@ -20,10 +20,10 @@ fi
 shell_scripts="$(fd .sh | xargs)"
 
 # The files we need to check all either end in .sh or else they're the files
-# in framework/cmd.d and framework/shims.  -x instructs shellcheck to also
+# in diachron/cmd.d and diachron/shims.  -x instructs shellcheck to also
 # check `source`d files.
 
-shellcheck -x --exclude="$exclusions" "$DIR/cmd" "$DIR"/framework/cmd.d/* "$DIR"/framework/shims/* "$shell_scripts"
+shellcheck -x --exclude="$exclusions" "$DIR/cmd" "$DIR"/diachron/cmd.d/* "$DIR"/diachron/shims/* "$shell_scripts"
 
 pushd "$DIR/master"
 docker run --rm -v $(pwd):/app -w /app golangci/golangci-lint:$golangci_lint golangci-lint run