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>

android/app/proguard-rules.pro

@@ -0,0 +1,4 @@
+# zxing-android-embedded reflects into CaptureActivity subclasses; keep the
+# whole client package rather than chasing individual members.
+-keep class com.journeyapps.barcodescanner.** { *; }
+-keep class com.google.zxing.** { *; }