_getCharacterList() had two bugs that silently dropped every
user-created persona from the group participant picker:
1. The /api/presets/templates endpoint returns a JSON array directly,
but the code read `data.templates` (always undefined). The forEach
over `data.templates || []` iterated over an empty array every time,
so no user templates were ever added.
2. Even if the array had been read correctly, the `t.isCharacter` guard
would have filtered them all out — user templates are saved by
presets.js without that flag, which is only present on built-in
PROMPT_TEMPLATES entries.
Fix: accept both the direct-array and the {templates:[]} shapes, drop
the isCharacter guard (user_templates are personas by definition), and
use the correct field name (system_prompt, not prompt) so the character
prompt actually reaches the group chat.
Fixes#1656
12fd8b6570