internaluploader: server + docs

One-way upload server: authentik SSO pairing (QR + app-initiated deep
link), hashed device tokens, streamed sha256-verified uploads into the
metube directory as <sha256>.<ext>.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/build.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+# Build and push the server image. Tag = <date>-<git sha>, matching the
+# convention of the other mysources.co.uk images (e.g. authentik-qr-login).
+set -euo pipefail
+cd "$(dirname "$0")"
+
+REGISTRY="mysources.co.uk/michal"
+NAME="internaluploader-server"
+TAG="$(date +%Y%m%d)-$(git rev-parse --short=12 HEAD)"
+IMAGE="${REGISTRY}/${NAME}:${TAG}"
+
+podman build -t "${IMAGE}" .
+podman push "${IMAGE}"
+echo "pushed ${IMAGE}"