Initial scaffold: blob store server, CLI scripts, and PWA share target

Clipboard/screenshot sync across own devices via a single DEVICE_TOKEN-gated
blob store, plus a small installable web app so a phone can push/pull
clips and share screenshots via the OS share sheet.

cli/scrot-onboard

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# Prints (and, if qrencode is installed, renders as a terminal QR code) the
+# onboarding link for the scrot PWA: opening it on a phone saves the device
+# token (via app.js's #t= handler) and, once the app is added to the home
+# screen, enables "Share to scrot" from the OS share sheet.
+set -euo pipefail
+
+: "${SCROT_SERVER:?set SCROT_SERVER, e.g. https://scrot.example.com}"
+: "${DEVICE_TOKEN:?set DEVICE_TOKEN}"
+
+url="$SCROT_SERVER/#t=$DEVICE_TOKEN"
+
+echo "$url"
+echo
+
+if command -v qrencode >/dev/null 2>&1; then
+  qrencode -t ANSIUTF8 "$url"
+else
+  echo "(install qrencode to render this as a scannable QR code in-terminal)"
+fi
+
+cat <<'EOF'
+
+On the phone:
+  1. Open the link/QR above — saves the device token, this device is now onboarded.
+  2. Add scrot to the home screen (share/menu -> "Add to Home Screen").
+  3. Reopen from the home screen icon once — this re-fetches the manifest
+     with the token baked into the share target, enabling "Share to scrot"
+     from the OS share sheet (photos, browser selection, etc).
+EOF