app: autorun mode (unattended run + upload + auto-exit); IPv6 severity rework

IPv6: absence is no longer a defect. If the network never provisioned v6
(no global address, no ::/0 route) the finding is ipv6.not_offered at INFO
(green) — most networks are still IPv4-only. If v6 IS advertised but
doesn't work, it's ipv6.broken at MEDIUM (yellow), because half-working v6
stalls connections. Verified on-device: our LAN advertises a v6 default
route with no path, and now reports ipv6.broken.

Autorun: `am start ... --ez autorun true` runs the suite immediately,
POSTs the report to the collection endpoint, shows the result for 3s and
finishes the activity (stays open if the upload failed). receiver.py gains
POST /report + GET /reports + GET /report/<name>. Verified end to end: one
adb command, report retrieved over HTTP, app closed itself.

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

echolot-app/app/build.gradle.kts

@@ -18,6 +18,10 @@ android {
         targetSdk = 36
         versionCode = 1
         versionName = "0.1.0"
+        // Automation: `adb shell am start -n app.echo_lot.app/.MainActivity --ez autorun true`
+        // runs a measurement immediately and POSTs the report here (dev collection endpoint).
+        buildConfigField("String", "REPORT_UPLOAD_URL", "\"http://89.185.109.150:443/report\"")
+        buildConfigField("String", "REPORT_UPLOAD_SECRET", "\"D4OmG5gGJsElqVVbtYIZbR\"")
     }
     buildTypes {
         release { isMinifyEnabled = false }