fix(wallet): replace text-marker hack with proper raw event API (room.sendRaw + MsgLikeKind.Other)

- Add Timeline.sendRaw() to send custom Matrix events
- Add CustomEventContent type for receiving custom events
- Update TimelineEventContentMapper to handle MsgLikeKind.Other
- Update TimelineItemContentFactory to intercept payment events
- Rewrite DefaultPaymentEventSender to use sendRaw instead of text markers
- Update TimelineItemContentPaymentFactory to parse raw JSON
- Remove text-marker detection from TimelineItemContentMessageFactory
- Update tests to use raw event API
- Mark raw event SDK blocker as RESOLVED in BLOCKERS.md

Event type: co.sulkta.payment.request (reverse-domain format)
Status updates: co.sulkta.payment.status

Benefits:
- Proper Matrix protocol compliance
- No JSON embedded in text messages
- Events won't be indexed by search
- Clean separation from regular messages

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/timeline/Timeline.kt

@@ -71,6 +71,18 @@ interface Timeline : AutoCloseable {
         intentionalMentions: List<IntentionalMention>,
     ): Result<Unit>
 
+    /**
+     * Send a raw/custom event to the room.
+     *
+     * @param eventType The event type (e.g., "co.sulkta.payment.request")
+     * @param content The JSON content of the event
+     * @return Result indicating success or failure
+     */
+    suspend fun sendRaw(
+        eventType: String,
+        content: String,
+    ): Result<Unit>
+
     suspend fun editMessage(
         eventOrTransactionId: EventOrTransactionId,
         body: String,

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/timeline/item/event/EventContent.kt

@@ -118,3 +118,14 @@ data object LegacyCallInviteContent : EventContent
 data object CallNotifyContent : EventContent
 
 data object UnknownContent : EventContent
+
+/**
+ * Content for custom/unknown message-like events that we want to handle specially.
+ *
+ * @param eventType The Matrix event type (e.g., "co.sulkta.payment.request")
+ * @param rawJson The raw JSON content of the event, if available
+ */
+data class CustomEventContent(
+    val eventType: String,
+    val rawJson: String?,
+) : EventContent