feat(schemas): add content filter to SearchMessagesSchema

- Added 'content' as an optional field to allow searching for messages
  containing specific text.

src/schemas.ts

@@ -136,6 +136,7 @@ export const ListServersSchema = z.object({});
 export const SearchMessagesSchema = z.object({
   guildId: z.string().min(1, "guildId is required"),
   // Optional filters
+  content: z.string().optional(),
   authorId: z.string().optional(),
   mentions: z.string().optional(),
   has: z.enum(['link','embed','file','poll','image','video','sound','sticker','snapshot']).optional(),

src/toolList.ts

@@ -309,6 +309,7 @@ export const toolList = [
       type: "object",
       properties: {
         guildId: { type: "string", description: "The ID of the Discord server (guild) to search within" },
+        content: { type: "string", description: "Search for messages containing specific text" },
         authorId: { type: "string", description: "Filter messages by a specific user ID" },
         mentions: { type: "string", description: "Filter messages that mention a specific user ID" },
         has: { type: "string", description: "Filter messages that contain specific content types (e.g., link, embed, file, poll, image, video, sound, sticker, snapshot)" },