feat: paginate, sync, and display branched sessions (#563)

* mobile: 以 Desktop Sessions 作为聊天历史源

* mobile: 修复快速连接崩溃与无标题会话隐藏

* mobile: 对齐 Desktop 标题并恢复完整历史

* mobile: 分离 Desktop 存储 ID 与运行 Session ID

* mobile: 将新对话持久化为 Desktop Session

* mobile: 渲染 Desktop 本地媒体

* feat: 分页加载并同步当前会话

* fix: 显示分支会话名称与层级

* fix: align PR with upstream app contract

* fix: preserve upstream session RPC lifecycle

app/src/main/java/com/m57/hermescontrol/data/model/SessionListResponse.kt

@@ -19,6 +19,8 @@ data class SessionInfo(
     val preview: String? = null,
     val started_at: Double? = null,
     val source: String? = null,
+    val parent_session_id: String? = null,
+    val display_name: String? = null,
 )
 
 @Serializable

app/src/main/java/com/m57/hermescontrol/data/model/SessionTreeItem.kt

@@ -0,0 +1,51 @@
+package com.m57.hermescontrol.data.model
+
+data class SessionTreeItem(
+    val session: SessionInfo,
+    val depth: Int,
+    val branchStem: String?,
+    val displayTitle: String,
+)
+
+fun flattenSessionTree(sessions: List<SessionInfo>): List<SessionTreeItem> {
+    val ids = sessions.mapTo(mutableSetOf()) { it.id }
+    val children = sessions.groupBy { it.parent_session_id?.takeIf(ids::contains) }
+    val result = mutableListOf<SessionTreeItem>()
+    val visited = mutableSetOf<String>()
+
+    fun append(
+        session: SessionInfo,
+        depth: Int,
+        branchStem: String?,
+        siblingIndex: Int,
+    ) {
+        if (!visited.add(session.id)) return
+        val isBranch = session.parent_session_id?.takeIf(ids::contains) != null
+        val title =
+            session.title?.takeIf(String::isNotBlank)
+                ?: session.display_name?.takeIf(String::isNotBlank)
+                ?: if (isBranch) {
+                    "branch ${siblingIndex + 1}"
+                } else {
+                    session.preview?.takeIf(String::isNotBlank)?.take(80) ?: "Untitled"
+                }
+        result += SessionTreeItem(session, depth, branchStem, title)
+        val descendants = children[session.id].orEmpty()
+        descendants.forEachIndexed { index, child ->
+            append(
+                session = child,
+                depth = depth + 1,
+                branchStem = if (index == descendants.lastIndex) "└─" else "├─",
+                siblingIndex = index,
+            )
+        }
+    }
+
+    children[null].orEmpty().forEachIndexed { index, root ->
+        append(root, depth = 0, branchStem = null, siblingIndex = index)
+    }
+    sessions.filterNot { it.id in visited }.forEachIndexed { index, orphan ->
+        append(orphan, depth = 0, branchStem = null, siblingIndex = index)
+    }
+    return result
+}