refactor: update dependencies and remove unused code

- Added new dependencies: `adler2`, `crc32fast`, `flate2`, `miniz_oxide`, and `libredox`.
- Updated existing dependencies: `tokio-rustls` to version 0.26.4 and `filetime` to version 0.2.27.
- Removed the `backup.rs` file as it is no longer needed.
- Introduced tests for configuration and credential management.
- Enhanced the `identity` module to generate W3C compliant DID documents.

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

scripts/test-stability-72h.sh

@@ -60,13 +60,13 @@ check_health() {
 
   # 3. RPC responds
   local rpc_resp
-  rpc_resp=$(rpc "system.info" 2>/dev/null)
+  rpc_resp=$(rpc "server.echo" '{"message":"stability-check"}' 2>/dev/null)
   if ! echo "$rpc_resp" | grep -q '"result"'; then
     # Try re-login
     login
-    rpc_resp=$(rpc "system.info" 2>/dev/null)
+    rpc_resp=$(rpc "server.echo" '{"message":"stability-check"}' 2>/dev/null)
     if ! echo "$rpc_resp" | grep -q '"result"'; then
-      fail_log "RPC system.info failed after re-login"
+      fail_log "RPC server.echo failed after re-login"
       failures=$((failures + 1))
     fi
   fi