feat(android): UPnP picker foundation (UPnP slice 3/6)

UpnpRoute - narrow domain model for a discovered UPnP / DLNA
renderer. Carries the AVTransport + RenderingControl control URLs
the SOAP client uses.

CastApi - Retrofit interface for the new POST /api/cast/stream-token
endpoint (UPnP slice 2/6). Returns {token, exp, url} for the
selection path.

OutputRoute.fromUpnpRoute - companion factory that tags the route
with Protocol.UPNP. Subtitle is 'Manufacturer Model' or falls back
to 'Network speaker' when description fields are blank.

CHANGE_WIFI_MULTICAST_STATE manifest permission - install-time on
all API levels, no runtime prompt. Required for SSDP multicast
discovery.

Discovery + SOAP + integration land in follow-up commits.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

android/app/src/main/AndroidManifest.xml

@@ -10,6 +10,7 @@
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
     <uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES" />
     <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
+    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
 
     <application
         android:name=".MinstrelApplication"

android/app/src/main/java/com/fabledsword/minstrel/api/endpoints/CastApi.kt

@@ -0,0 +1,49 @@
+package com.fabledsword.minstrel.api.endpoints
+
+import kotlinx.serialization.Serializable
+import retrofit2.http.Body
+import retrofit2.http.POST
+
+/**
+ * Retrofit interface for the cast-token endpoint. Used by the UPnP
+ * selection path in `OutputPickerController` to obtain a signed stream
+ * URL that a network speaker can fetch without the user's session
+ * cookie — those devices cannot carry the session, so the signed
+ * query string is the only way they can fetch the bytes.
+ *
+ * Endpoint: `POST /api/cast/stream-token`
+ * Auth: standard session cookie (`AuthCookieInterceptor` handles it).
+ *
+ * Server contract lives at `internal/api/cast_token.go`
+ * (commit e774097f). Field names here mirror the server's `json:`
+ * tags verbatim — `trackId` / `expSeconds` — so no `@SerialName` is
+ * needed on the request, and `token` / `exp` / `url` map straight
+ * through on the response.
+ */
+interface CastApi {
+    @POST("api/cast/stream-token")
+    suspend fun streamToken(@Body req: StreamTokenRequest): StreamTokenResponse
+}
+
+/**
+ * Request body. [expSeconds] is clamped server-side to [60, 86400];
+ * the 21_600 default (6h) is long enough to play through any typical
+ * track without re-minting mid-playback.
+ */
+@Serializable
+data class StreamTokenRequest(
+    val trackId: String,
+    val expSeconds: Int = 21_600,
+)
+
+/**
+ * Response body. [url] is a fully-formed stream URL with [token] and
+ * [exp] already embedded as query params — callers pass it verbatim
+ * to `AVTransport.SetAVTransportURI`.
+ */
+@Serializable
+data class StreamTokenResponse(
+    val token: String,
+    val exp: Long,
+    val url: String,
+)

android/app/src/main/java/com/fabledsword/minstrel/player/output/OutputRoute.kt

@@ -1,6 +1,7 @@
 package com.fabledsword.minstrel.player.output
 
 import androidx.mediarouter.media.MediaRouter
+import com.fabledsword.minstrel.player.output.upnp.UpnpRoute
 
 /**
  * Narrow domain model for an audio output route. Independent of
@@ -68,5 +69,35 @@ data class OutputRoute(
                 isConnected = connected,
             )
         }
+
+        /**
+         * Lift a discovered UPnP renderer into the picker's domain
+         * model. Used by the UPnP discovery controller to merge
+         * network speakers into the same `OutputPickerController`
+         * routes stream the system routes come through.
+         *
+         * `isConnected = false` because UPnP devices have no
+         * MediaRouter connection-state concept — they're always
+         * "available" on the LAN, and the picker's selected-route
+         * rendering handles the "currently playing" indicator.
+         *
+         * Subtitle is `manufacturer modelName` joined by a single
+         * space, falling back to "Network speaker" when both fields
+         * are blank.
+         */
+        fun fromUpnpRoute(route: UpnpRoute): OutputRoute {
+            val description = listOfNotNull(
+                route.manufacturer.takeIf { it.isNotBlank() },
+                route.modelName.takeIf { it.isNotBlank() },
+            ).joinToString(" ").ifBlank { "Network speaker" }
+            return OutputRoute(
+                id = route.id,
+                name = route.name,
+                description = description,
+                kind = Kind.Other,
+                protocol = Protocol.UPNP,
+                isConnected = false,
+            )
+        }
     }
 }

android/app/src/main/java/com/fabledsword/minstrel/player/output/upnp/UpnpRoute.kt

@@ -0,0 +1,27 @@
+package com.fabledsword.minstrel.player.output.upnp
+
+import okhttp3.HttpUrl
+
+/**
+ * A discovered UPnP / DLNA MediaRenderer (Sonos, Yamaha MusicCast,
+ * Bose SoundTouch, generic DLNA renderers). Lifted out of the SOAP /
+ * SSDP details so the picker UI consumes a narrow domain shape.
+ *
+ * Generic UPnP only for THIS slice — Sonos-specific grouping value-adds
+ * (group join/leave, zone topology) live in a separate Sonos extension
+ * scoped in
+ * docs/superpowers/specs/2026-06-03-android-output-picker-upnp-scope.md.
+ *
+ * [id] is the device UDN (e.g. `uuid:RINCON_ABC...`). [name] is the
+ * raw `<friendlyName>` straight from the device description — callers
+ * fall back to "Network speaker" upstream when it's blank; this class
+ * does not perform that substitution itself.
+ */
+data class UpnpRoute(
+    val id: String,
+    val name: String,
+    val manufacturer: String,
+    val modelName: String,
+    val avTransportControlUrl: HttpUrl,
+    val renderingControlUrl: HttpUrl?,
+)