Add be9700-api: TP-Link BE9700 router API proxy + Scalar docs

apps/be9700-api/metadata/description.md

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+# BE9700 Router API
+
+A stateless Node.js proxy and interactive API documentation server for the
+**TP-Link BE9700 WiFi 7** router.
+
+## What it does
+
+- Exposes the router's internal API as a clean, resource-oriented REST surface
+  (`/api/*`) covering **203 endpoints** across wireless bands (2.4 GHz / 5 GHz /
+  6 GHz), LAN/DHCP, NAT, UPnP, system time, and diagnostics.
+- Serves **interactive Scalar API docs** at `/docs` — explore and try every
+  endpoint directly in the browser.
+- Returns the OpenAPI 3.1 specification at `/openapi.json` for use with any
+  compatible tooling.
+- Health/status JSON at `/`.
+
+## Stateless header-auth model
+
+No router credentials are stored in the container or in Runtipi form fields.
+Every request to `/api/*` must carry:
+
+| Header | Purpose |
+|--------|---------|
+| `X-Router-Host` | Router IP or hostname (e.g. `192.168.0.1`) |
+| `X-Router-Password` | Router admin password (for fresh sessions) |
+| `X-Router-Session` | Reuse a session token returned by a previous call (JSON) |
+
+This means the container itself holds no secrets and is safe to expose via
+Traefik without any additional auth middleware — just use the API from clients
+that supply the headers.
+
+## Quick start
+
+Once installed, open the **Scalar docs** at `http://<your-server>:8347/docs`
+and authenticate each request with the `X-Router-Host` and
+`X-Router-Password` headers.
+
+## Source
+
+`https://git.alexzaw.dev/alexz/be9700-api`