refactor(chatbot): drop static server-stats context, go fully tool-based

The chatbot already had an agentic tool loop (get_server_stats,
get_top_channels, get_recent_activity, get_top_flagged), but processMessage
still baked a serverInsights snapshot into the system prompt and told the
model to "answer from that data". That defeats the tools: the model answered
from a stale snapshot instead of living numbers, and the guild/channel scope
the frontend sends was never forwarded to the tools.

Changes (services/backend/src/modules/chatbot):
- Remove getServerInsights() + ServerInsights (dead after this change).
- buildSystemPrompt(): drop the hardcoded stats block; instruct the model it
  has NO memorized server numbers and MUST call a tool for any server-data
  question, answering only from tool results.
- processMessage(): stop fetching insights; pass the request guildId/channelId
  scope through to callLLM.
- callLLM(): accept scope; auto-fill empty guildId/channelId on tool calls from
  the request scope so the model never has to guess IDs and tools always query
  the right server.

Behavior: answers now come from live DB data via tools, scoped to the server
the user is chatting in. tsc + biome + 36 backend tests green.

Co-Authored-By: Claude Opus 5 (Nous Research)

services/backend/src/modules/chatbot/chatbot.repository.ts

@@ -31,13 +31,6 @@ export interface ChatbotHistoryRow {
   created_at: string;
 }
 
-export interface ServerInsights {
-  total_messages: number;
-  active_users: number;
-  flagged: number;
-  warned: number;
-}
-
 export class ChatbotRepository {
   async saveConversation(input: SaveConversationInput): Promise<void> {
     const db = getDatabase();
@@ -83,56 +76,6 @@ export class ChatbotRepository {
       "Chat history cleared",
     );
   }
-
-  async getServerInsights(
-    guildId?: string,
-    channelId?: string,
-  ): Promise<ServerInsights> {
-    try {
-      const db = getDatabase();
-      const conditions: SQL[] = [];
-
-      if (guildId) {
-        conditions.push(eq(pgMessagesTable.guild_id, guildId));
-      }
-      if (channelId) {
-        conditions.push(eq(pgMessagesTable.channel_id, channelId));
-      }
-
-      const where = conditions.length > 0 ? and(...conditions) : undefined;
-
-      const [result] = await db
-        .select({
-          total_messages: sql<number>`COUNT(*)::int`,
-          active_users: sql<number>`COUNT(DISTINCT ${pgMessagesTable.user_id})::int`,
-          flagged: sql<number>`COUNT(*) FILTER (WHERE ${pgMessagesTable.ai_status} = 'flagged')::int`,
-          warned: sql<number>`COUNT(*) FILTER (WHERE ${pgMessagesTable.ai_status} = 'warn')::int`,
-        })
-        .from(pgMessagesTable)
-        .where(where);
-
-      const insights = result ?? {
-        total_messages: 0,
-        active_users: 0,
-        flagged: 0,
-        warned: 0,
-      };
-
-      logger.debug({ guildId, channelId, insights }, "Server insights fetched");
-      return insights;
-    } catch (error) {
-      logger.warn(
-        { error, guildId, channelId },
-        "Failed to load server insights",
-      );
-      return {
-        total_messages: 0,
-        active_users: 0,
-        flagged: 0,
-        warned: 0,
-      };
-    }
-  }
 }
 
 export const chatbotRepository = new ChatbotRepository();