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>

diachron/cmd.d/node

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+set -eu
+
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+exec "$DIR"/../shims/node "$@"