Add new admin panel, failover, dns fallback, providers, limiters. Update XHTTP

service/admin_panel/README.md

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+# admin_panel
+
+A TypeScript (Vite + React + Material UI, dark theme) admin panel that talks to
+the `manager_api/http` server.
+
+The compiled SPA is **embedded into the Go binary via `//go:embed`** — the
+post-processed `dist/` directory is checked into the repo, so
+`go build -tags with_admin_panel ./cmd/sing-box` produces a fully
+self-contained binary with no Node.js required at compile time.
+
+The `web/` directory holds the original TypeScript sources, which are only
+needed when the panel itself is being modified. `make admin_panel_regen`
+rebuilds `dist/` from those sources via `npm run build` followed by an
+in-place post-processing step (`cmd/internal/admin_panel_pack`).
+
+## Layout
+
+```
+service/admin_panel/
+├── service.go         # Go service (build tag: with_admin_panel, //go:embed dist)
+├── service_stub.go    # Stub when the tag is missing
+├── service_test.go    # Tests for the SPA handler
+├── dist/              # Embedded SPA bytes (committed to git)
+│   ├── index.html
+│   ├── index.html.gz
+│   └── assets/
+│       ├── index-*.js
+│       ├── index-*.js.gz
+│       ├── index-*.css
+│       ├── index-*.css.gz
+│       └── inter-*.woff2
+└── web/               # Vite + React TypeScript source (only needed to regen)
+    ├── package.json
+    ├── vite.config.ts
+    ├── tsconfig.json
+    ├── index.html
+    └── src/
+        ├── main.tsx
+        ├── App.tsx
+        ├── theme.ts
+        ├── api/{client,types}.ts
+        ├── auth/AuthContext.tsx
+        ├── components/{Layout,CrudPage}.tsx
+        └── pages/*.tsx
+
+cmd/internal/admin_panel_pack/
+└── main.go            # Post-processor: drops .woff, rewrites CSS, pre-gzips text
+```
+
+## Building sing-box with the panel
+
+`dist/` is committed, so any developer or CI machine can build a
+self-contained binary with no Node.js / npm available:
+
+```bash
+go build -tags with_admin_panel ./cmd/sing-box
+# or
+make build_admin_panel
+```
+
+If the tag is omitted the service registers a stub that errors out on start.
+
+## Regenerating dist/
+
+Whenever the SPA source under `web/` is changed, run:
+
+```bash
+make admin_panel_regen
+```
+
+That target performs two steps:
+
+1. `make admin_panel_web` — `npm install` + `npm run build` in `web/`,
+   producing `service/admin_panel/dist/`.
+2. `make admin_panel_pack` — runs the
+   `cmd/internal/admin_panel_pack` post-processor, which:
+   - deletes the legacy `*.woff` (WOFF 1.0) fallback fonts; every browser
+     since 2014 reads WOFF2 natively, and shipping both formats roughly
+     doubles the embedded font payload;
+   - rewrites the bundled `*.css` to drop `,url(...).woff) format("woff")`
+     references so the @font-face rules don't point at files that aren't
+     shipped;
+   - drops a gzip-compressed `*.gz` companion next to every text-like
+     asset (.html, .css, .js, .svg, .json) at `gzip.BestCompression`. The
+     runtime serves those bytes verbatim with `Content-Encoding: gzip`
+     when the client advertises gzip support, and falls back to the raw
+     file otherwise.
+
+After the post-processing pass, commit the resulting `dist/` directory
+along with your source changes.
+
+## Configuring sing-box
+
+Add a service entry of type `admin-panel`:
+
+```json
+{
+  "services": [
+    {
+      "type": "admin-panel",
+      "tag": "admin",
+      "listen": "127.0.0.1",
+      "listen_port": 8081
+    }
+  ]
+}
+```
+
+The panel itself does not require any back-end auth: at sign-in the user
+enters the URL and bearer key of a `manager-api` instance. Both are stored
+only in the browser's `localStorage`.