refactor: simplify server stats widget system

Replaced complex drag-and-drop grid layout with simple checkbox-based
configuration and static responsive grid display.

- Removed react-grid-layout dependency and 6 related packages
- Simplified StatsConfig from complex Widget objects to simple array
- Added Statistics tab in HostManagerEditor for checkbox selection
- Refactored Server.tsx to use CSS Grid instead of ResponsiveGridLayout
- Simplified widget components by removing edit mode and size selection
- Deleted unused AddWidgetDialog and registry files
- Fixed statsConfig serialization in backend routes

Net result: -787 lines of code, cleaner architecture.

package-lock.json

@@ -35,7 +35,6 @@
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         "@types/multer": "^2.0.0",
         "@types/qrcode": "^1.5.5",
-        "@types/react-grid-layout": "^1.3.5",
         "@types/speakeasy": "^2.0.10",
         "@uiw/codemirror-extensions-langs": "^4.24.1",
         "@uiw/react-codemirror": "^4.24.1",
@@ -69,7 +68,6 @@
         "qrcode": "^1.5.4",
         "react": "^19.1.0",
         "react-dom": "^19.1.0",
-        "react-grid-layout": "^1.5.2",
         "react-h5-audio-player": "^3.10.1",
         "react-hook-form": "^7.60.0",
         "react-i18next": "^15.7.3",
@@ -3895,15 +3893,6 @@
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       }
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-      "license": "MIT",
-      "dependencies": {
-        "@types/react": "*"
-      }
-    },
     "node_modules/@types/responselike": {
       "version": "1.0.3",
       "dev": true,
@@ -7302,12 +7291,6 @@
       "version": "3.1.3",
       "license": "MIT"
     },
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       "dev": true,
@@ -11588,38 +11571,6 @@
         "react": "^19.1.1"
       }
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-        "react-dom": ">= 16.3.0"
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     "node_modules/react-h5-audio-player": {
       "version": "3.10.1",
       "license": "MIT",
@@ -11828,19 +11779,6 @@
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-        "react": ">= 16.3"
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     "node_modules/react-resizable-panels": {
       "version": "3.0.6",
       "license": "MIT",
@@ -12185,12 +12123,6 @@
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-      "license": "MIT"
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     "node_modules/resolve-alpn": {
       "version": "1.2.1",
       "dev": true,