Inference: support wildcard .txt files and fix nested wildcard syntax

Source: Discord feature-requests thread (Sep 14, 2026).

Request: support wildcard .txt files in the Inference tab, matching behavior users expect from A1111/ComfyUI dynamic prompts.

Additionally reported: nested wildcard syntax breaks in Inference. Example that fails:

{{short|long} dress,|{white|yellow|green} sweater,|t-shirt,}

Normally the entire nested structure should resolve as a dynamic prompt, but the nested braces break the wildcard parser.

Discord thread: https://discord.com/channels/1115555685476868168/1239192894191964161 (related active thread 'Wildcarding in the inference tab')