#1 feat: add configurable Enter key behavior for message input

- Add enterKeyBehavior setting to config schema (shift-enter-send | enter-send)
- Implement Enter key behavior toggle in SettingsControls component
- Update ChatInput to respect user's Enter key preference
- Support IME composition to prevent accidental sends during Japanese input
- Add dynamic placeholder text based on selected behavior

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/server/config/config.ts

@@ -3,6 +3,7 @@ import z from "zod";
 export const configSchema = z.object({
   hideNoUserMessageSession: z.boolean().optional().default(true),
   unifySameTitleSession: z.boolean().optional().default(true),
+  enterKeyBehavior: z.enum(["shift-enter-send", "enter-send"]).optional().default("shift-enter-send"),
 });
 
 export type Config = z.infer<typeof configSchema>;