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/build.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    id("com.android.application") version "8.11.1" apply false
+    id("org.jetbrains.kotlin.android") version "2.1.21" apply false
+    id("com.google.devtools.ksp") version "2.1.21-2.0.1" apply false
+}