app: link.ra_source router identification + brand icons + DEV build variant

link.ra_source answers "who advertises IPv6 here, and which box is it":
RA source per network, MAC recovered from the modified-EUI-64 link-local
(privacy addresses reported as such, not guessed), vendor via a curated
OUI table, UPnP/SSDP M-SEARCH for the gateway's server banner + device
description (manufacturer/model/friendly name), and reverse DNS. All SSDP
responders are recorded so a rogue RA sender that isn't the gateway can
still be matched; the MAC accompanies every identity source as the hook
for future LLDP/mDNS cross-matching. UI gains a "Router / IPv6 advertiser"
panel.

Icons: branding adaptive icon converted to vector drawables (+ PNG
mipmaps, monochrome layer). The debug build is now a separate app —
applicationIdSuffix .dev, label "Echolot DEV", DEV-badged icon — so it
installs alongside a production build and can't be confused with it.

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

echolot-app/app/src/debug/res/drawable/ic_launcher_foreground_dev.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- SPDX-License-Identifier: GPL-3.0-or-later
+     Debug foreground: the production mark with a DEV ribbon so the dev build is
+     unmistakable on the launcher next to a real install. -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@drawable/ic_launcher_foreground"/>
+    <item android:drawable="@drawable/ic_dev_badge"/>
+</layer-list>

echolot-app/app/src/debug/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@drawable/ic_launcher_background"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground_dev"/>
+</adaptive-icon>

echolot-app/app/src/debug/res/mipmap-anydpi-v26/ic_launcher_round.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@drawable/ic_launcher_background"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground_dev"/>
+</adaptive-icon>

echolot-app/app/src/debug/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">Echolot DEV</string>
+</resources>