feat(#532): add process.list + process.kill manager screen (#556)

Co-authored-by: M57 <m57@hermes-control.app>

app/src/main/java/com/m57/hermescontrol/data/session/ActiveSessionHolder.kt

@@ -0,0 +1,28 @@
+package com.m57.hermescontrol.data.session
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+
+/**
+ * App-wide mirror of the active chat session id.
+ *
+ * The desktop `process.list` / `process.kill` RPCs are session-scoped — the
+ * gateway returns `4001 "session not found"` without a valid `session_id`, and
+ * mobile has no global "current session" holder (ChatViewModel keeps it
+ * privately). This singleton holds the last-known active session id so
+ * session-scoped drawer screens (e.g. the Processes screen, issue #532) can
+ * issue those RPCs. ChatViewModel writes here on every switch/resume; it is a
+ * best-effort mirror and may be null when no chat session has been opened yet.
+ */
+object ActiveSessionHolder {
+    private val _activeSessionId = MutableStateFlow<String?>(null)
+
+    /** The currently active chat session id, or null if none is known yet. */
+    val activeSessionId: StateFlow<String?> = _activeSessionId.asStateFlow()
+
+    /** Update the active session id. Pass null to clear (e.g. on logout). */
+    fun set(sessionId: String?) {
+        _activeSessionId.value = sessionId
+    }
+}