feat(odin): conversation-scoped service + routes (replace /history)

Remove single-thread getChatHistory/appendChatMessages/clearChatHistory and the
three /history routes; add listConversations, createConversation, getConversation-
Messages, appendConversationMessages, renameConversation, deleteConversation with
ownership checks and auto-title; wire six /conversations[/:id] routes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/schemas/ai.schema.ts

@@ -24,6 +24,14 @@ export const AiHistoryAppendSchema = z.object({
     .max(20, "Příliš mnoho zpráv"),
 });
 
+export const AiCreateConversationSchema = z.object({
+  title: z.string().max(255).optional(),
+});
+
+export const AiRenameConversationSchema = z.object({
+  title: z.string().min(1, "Název je povinný").max(255),
+});
+
 export const AiBudgetSchema = z.object({
   budget_usd: z
     .union([z.number(), z.string()])