Add drawer menu with flat structure, unified panel styling, Room/SQLCipher setup

app/src/main/java/com/mistral/chat/ui/SessionsAdapter.kt

@@ -0,0 +1,45 @@
+package com.mistral.chat.ui
+
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.ImageView
+import android.widget.TextView
+import androidx.recyclerview.widget.RecyclerView
+import com.mistral.chat.R
+import com.mistral.chat.data.Session
+
+class SessionsAdapter(
+    private val sessions: List<Session>,
+    private val getCurrentSessionId: () -> Long?,
+    private val onSessionClick: (Session) -> Unit,
+    private val onSessionLongClick: (Session) -> Unit
+) : RecyclerView.Adapter<SessionsAdapter.ViewHolder>() {
+
+    class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
+        val title: TextView = view.findViewById(R.id.sessionTitle)
+        val checkmark: ImageView = view.findViewById(R.id.sessionCheckmark)
+    }
+
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
+        val view = LayoutInflater.from(parent.context)
+            .inflate(R.layout.item_session, parent, false)
+        return ViewHolder(view)
+    }
+
+    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
+        val session = sessions[position]
+        val currentId = getCurrentSessionId()
+        holder.title.text = session.title
+        holder.title.alpha = if (session.id == currentId) 1.0f else 0.7f
+        holder.checkmark.visibility = if (session.id == currentId) View.VISIBLE else View.GONE
+        
+        holder.itemView.setOnClickListener { onSessionClick(session) }
+        holder.itemView.setOnLongClickListener {
+            onSessionLongClick(session)
+            true
+        }
+    }
+
+    override fun getItemCount(): Int = sessions.size
+}