feat(bot): replace maxTokens with contextMessages option

- Switched `maxTokens` to `contextMessages` to set chat history length instead of token limit.
- Updated environment variables, NixOS module, and prompt building logic for consistency.
- Removed in-memory conversation history, now fetching from Nextcloud for better scalability.

systems/x86_64-linux/mx/nextcloud-claude-bot/module.nix

@@ -56,12 +56,12 @@ in {
       description = "Nextcloud usernames allowed to talk to the bot (empty = all)";
     };
     
-    maxTokens = mkOption {
+    contextMessages = mkOption {
       type = types.int;
-      default = 4096;
-      description = "Max tokens for Claude response";
+      default = 6;
+      description = "Number of recent messages to fetch from chat for context";
     };
-    
+
     timeout = mkOption {
       type = types.int;
       default = 120;
@@ -89,7 +89,7 @@ in {
         NEXTCLOUD_URL = cfg.nextcloudUrl;
         CLAUDE_PATH = cfg.claudePath;
         ALLOWED_USERS = concatStringsSep "," cfg.allowedUsers;
-        MAX_TOKENS = toString cfg.maxTokens;
+        CONTEXT_MESSAGES = toString cfg.contextMessages;
         TIMEOUT = toString cfg.timeout;
         SYSTEM_PROMPT = cfg.systemPrompt or "";
         PYTHONPATH = botModule;