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/core-measurement/src/main/kotlin/app/echo_lot/measurement/Test.kt

@@ -55,6 +55,8 @@ object TestType {
     const val LINK_SNAPSHOT = "link.snapshot"
     const val LINK_DHCP_RENEWAL_WATCH = "link.dhcp_renewal_watch"
     const val LINK_IP_MONITOR = "link.ip_monitor"
+    /** Who advertises IPv6 on this link (+ gateway identity). Registry addition, v1.1. */
+    const val LINK_RA_SOURCE = "link.ra_source"
     // net — connectivity validation (reproduces Android's NetworkMonitor generate_204 checks)
     const val NET_CAPTIVE_PORTAL = "net.captive_portal"
     // icmp