fix(discovery): use protobufs Maven dep after rebase onto #5675

#5275 created :feature:discovery with implementation(projects.core.proto), but
main's #5675 replaced the :core:proto submodule with the org.meshtastic:protobufs
Maven artifact. Rebasing left a stale module reference. Switched to
implementation(libs.meshtastic.protobufs), matching the convention (cf. feature/node).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jamesarich

feature/discovery/build.gradle.kts

@@ -41,13 +41,13 @@ kotlin {
             implementation(projects.core.navigation)
             implementation(projects.core.network)
             implementation(projects.core.prefs)
-            implementation(projects.core.proto)
             implementation(projects.core.repository)
             implementation(projects.core.resources)
             implementation(projects.core.service)
             implementation(projects.core.ui)
 
             implementation(libs.kotlinx.collections.immutable)
+            implementation(libs.meshtastic.protobufs)
         }
 
         commonTest.dependencies { implementation(projects.core.testing) }