Custom RTMP saved accounts, RTMP test server, composition pipeline

- Backend: POST /providers/accounts/custom-rtmp to save reusable RTMP servers
- Backend: Encrypt rtmpUrl/streamKey in existing token fields, decrypt on GET
- Backend: Skip token revocation on DELETE for CUSTOM_RTMP accounts
- Backend: Decrypt CUSTOM_RTMP credentials into destinations on plan create/update
- Android: Add rtmpUrl/streamKey to LinkedAccount entity + shared parcelable (Room v6)
- Android: Add Custom RTMP dialog in AccountsScreen, auto-fill in plan destination picker
- Android: Handle CUSTOM_RTMP accounts in CreatePlanViewModel.loadExistingPlan
- Add local RTMP test server (tools/rtmp-server.js) with auto-ffplay on publish
- Add composition pipeline native code

shared/src/main/java/com/omixlab/lckcontrol/shared/LinkedAccount.kt

@@ -11,6 +11,8 @@ data class LinkedAccount(
     val avatarUrl: String? = null,
     val isAuthenticated: Boolean = false,
     val isEnabled: Boolean = true,
+    val rtmpUrl: String? = null,
+    val streamKey: String? = null,
 ) : Parcelable {
 
     constructor(parcel: Parcel) : this(
@@ -21,6 +23,8 @@ data class LinkedAccount(
         avatarUrl = parcel.readString(),
         isAuthenticated = parcel.readInt() != 0,
         isEnabled = if (parcel.dataAvail() > 0) parcel.readInt() != 0 else true,
+        rtmpUrl = if (parcel.dataAvail() > 0) parcel.readString() else null,
+        streamKey = if (parcel.dataAvail() > 0) parcel.readString() else null,
     )
 
     override fun writeToParcel(parcel: Parcel, flags: Int) {
@@ -31,6 +35,8 @@ data class LinkedAccount(
         parcel.writeString(avatarUrl)
         parcel.writeInt(if (isAuthenticated) 1 else 0)
         parcel.writeInt(if (isEnabled) 1 else 0)
+        parcel.writeString(rtmpUrl)
+        parcel.writeString(streamKey)
     }
 
     override fun describeContents(): Int = 0