fix(tui): insert skill name without wiping existing prompt text

When selecting a skill from the TUI skill picker, the skill name is now
inserted at the cursor position using input.insertText() instead of
replacing the entire prompt with input.setText().

Previously, typing a question then selecting a skill would destructively
wipe the entire prompt.

Closes: #27578
Closes: #27160
Closes: #18756
Closes: #18755

Author: HaleTom

packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx

@@ -587,12 +587,9 @@ export function Prompt(props: PromptProps) {
           dialog.replace(() => (
             <DialogSkill
               onSelect={(skill) => {
-                input.setText(`/${skill} `)
-                setStore("prompt", {
-                  input: `/${skill} `,
-                  parts: [],
-                })
-                input.gotoBufferEnd()
+                input.insertText(`/${skill} `)
+                setStore("prompt", "input", input.plainText)
+                syncExtmarksWithPromptParts()
               }}
             />
           ))