feat: add admin panel at /admin for full dashboard configuration

- Backend: ConfigManager write methods (atomic YAML save), admin CRUD
  router for settings (display/odoo/refresh) and nodes, WS broadcast
  on config changes, fix nmap scan blocking event loop with to_thread
- Frontend: admin UI with tab navigation, overview dashboard, node
  CRUD table with modal form, Odoo/display/refresh settings pages,
  typed API wrappers, active views filtering, config_changed WS handler
- Infra: nginx no-cache headers for HTML, cache-forever for hashed assets
- Fixes: WebSocket reconnect loop (ref pattern), rotation index OOB
  when views shrink, mutable node list cache

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

backend/modules/config_manager.py

@@ -1,3 +1,4 @@
+import os
 from pathlib import Path
 from typing import Any
 
@@ -18,6 +19,12 @@ class ConfigManager:
         with open(p) as f:
             return yaml.safe_load(f) or {}
 
+    def _save_yaml(self, path: str, data: dict[str, Any]) -> None:
+        tmp = path + ".tmp"
+        with open(tmp, "w") as f:
+            yaml.dump(data, f, default_flow_style=False, allow_unicode=True, sort_keys=False)
+        os.replace(tmp, path)
+
     def get_settings(self) -> dict[str, Any]:
         if not self._settings:
             self._settings = self._load_yaml(self._settings_path)
@@ -26,7 +33,7 @@ class ConfigManager:
     def get_nodes(self) -> list[dict[str, Any]]:
         if not self._services:
             self._services = self._load_yaml(self._services_path)
-        return self._services.get("nodes", [])
+        return list(self._services.get("nodes", []))
 
     def get_node_by_ip(self, ip: str) -> dict[str, Any] | None:
         for node in self.get_nodes():
@@ -39,6 +46,21 @@ class ConfigManager:
             self._services = self._load_yaml(self._services_path)
         return self._services.get("network_scan", {})
 
+    def update_settings(self, section: str, values: dict[str, Any]) -> dict[str, Any]:
+        settings = self._load_yaml(self._settings_path)
+        if section not in settings:
+            settings[section] = {}
+        settings[section].update(values)
+        self._save_yaml(self._settings_path, settings)
+        self._settings = {}
+        return settings[section]
+
+    def save_nodes(self, nodes: list[dict[str, Any]]) -> None:
+        services = self._load_yaml(self._services_path)
+        services["nodes"] = nodes
+        self._save_yaml(self._services_path, services)
+        self._services = {}
+
     def reload(self) -> None:
         self._settings = {}
         self._services = {}