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

apps/be9700-api/build/README.md

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+# be9700-api — Build Notes
+
+## Image
+
+`git.alexzaw.dev/alexz/be9700-api:<tag>`
+
+## Source
+
+`/home/alexz/be9700-api` (also mirrored to `https://git.alexzaw.dev/alexz/be9700-api`)
+
+The Dockerfile lives in the root of the source directory alongside `server.js`.
+
+## Architecture
+
+- **amd64 only** — the app is pure Node.js (no native addons) but the image is
+  only built and tested on the amd64 host. Add `--platform linux/arm64` to the
+  build command and push a separate tag to add arm64 support.
+
+## Security
+
+`.dockerignore` excludes `.env`, `.env.*`, `.git`, `scripts/`, `*.log`, `*.curl`,
+`network-captures.js`. The image contains no router credentials.
+
+## Build
+
+```bash
+# From this directory:
+bash build.sh
+
+# Or with overrides:
+IMAGE_TAG=1.0.1 bash build.sh --no-cache
+```
+
+Requires the Docker daemon to be authenticated to `git.alexzaw.dev`.