feat(dynamicprompts): support wildcards and prevent hang on unknown wildcards

[Pfannkuchensack]

Summary

Wire up dynamicprompts' WildcardManager so __name__ references resolve against .txt files in a new wildcards/ directory (configurable via the wildcards_dir setting). Both the /utilities/dynamicprompts endpoint and the DynamicPrompt node now build the manager from this path.

Referencing an unknown wildcard previously hung the combinatorial generator forever: its not-found fallback yields the wrapped wildcard infinitely, and the variant dedup logic discards those duplicates without ever advancing. This froze the UI prompt preview. Unknown wildcards are now detected up front and reported as a clear error instead of attempting generation.

Related Issues / Discussions

N/A — reported by a user whose dynamic prompt ({__random__8chan|fenster|stuff}) froze the prompt preview. The __random__ was parsed as a wildcard reference rather than literal text.

#9137 adds wildcard too.

QA Instructions

Hang fix (the actual bug):

1. Open the canvas/generation tab and enter a prompt containing an unknown wildcard, e.g. {__random__a|b|c}.
2. Before this change the dynamic prompts preview spinner would hang indefinitely (the request never returned).
3. After this change the preview returns immediately and shows the error: No values found for wildcard(s): random.

Wildcard feature:

1. Create a wildcard file under <invokeai_root>/wildcards/animals.txt with one value per line:

   cat
   dog
   bird
   

2. Use __animals__ in a prompt (also works inside variants, e.g. a {__animals__|house}).
3. Confirm the preview/generation expands it to the wildcard values. Subdirectories map to __subdir/name__.
4. The wildcards/ directory is created automatically on first use; the location is configurable via the wildcards_dir setting.

Automated tests:

pytest tests/app/util/test_dynamicprompts.py tests/app/routers/test_utilities.py

Merge Plan

Standard merge — no special handling required. Changes are additive and backwards-compatible:

• New wildcards_dir config setting (defaults to wildcards/); no migration needed.
• No DB schema or redux slice changes.
• docs/src/generated/settings.json was regenerated to include the new setting.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration — N/A, no slice changes
• Documentation added / updated (if applicable) — regenerated settings.json
• Updated What's New copy (if doing a release after this PR)