Set OpenAI Responses store false for AI chat and agents (#20888)

## Summary

This PR sets `openai.store = false` for Twenty's `@ai-sdk/openai` AI
calls.

This follows the approach discussed in #20877: instead of adding a new
Twenty-specific Zero Data Retention config variable, OpenAI Responses
calls no longer rely on OpenAI-stored response/item references. This
should help Zero Data Retention organizations and may also avoid stale
persisted-item replay errors for non-ZDR OpenAI users.

Changes included:

- Adds a shared OpenAI provider-options helper that merges `openai.store
= false` for `@ai-sdk/openai` models.
- Applies the helper to AI chat `streamText` calls.
- Applies the helper to workflow/agent `generateText` calls.
- Preserves OpenAI encrypted reasoning metadata through DB/UI message
mappers so reasoning context can be replayed without stored OpenAI item
references.
- Does not add a new env/config variable.

Related to issue #20877.

## Behavior / Tradeoffs

This changes OpenAI Responses behavior for all Twenty OpenAI users, not
only ZDR users.

The intended benefit is that Twenty no longer depends on OpenAI-stored
response/item references. The main tradeoff is reduced provider-side
item-reference reuse for non-ZDR OpenAI users.

To reduce the impact for reasoning models, this PR preserves
`providerMetadata.openai.reasoningEncryptedContent` through message
persistence/replay so reasoning context can still be provided without
stored OpenAI item references.

## Tests

- Focused server Jest tests for OpenAI provider-options merging and
reasoning metadata mapping.
- Focused frontend Jest test for reasoning metadata mapping.
- `oxlint` and `oxfmt --check` on changed files.
- `git diff --check`.

---------

Co-authored-by: Charles Bochet <charles@twenty.com>
Co-authored-by: Etienne <45695613+etiennejouan@users.noreply.github.com>

packages/twenty-front/src/modules/ai/utils/mapDBPartToUIMessagePart.ts

@@ -23,6 +23,7 @@ export const mapDBPartToUIMessagePart = (
         type: 'reasoning',
         text: part.reasoningContent!,
         state: part.state as ReasoningUIPart['state'],
+        providerMetadata: part.providerMetadata ?? undefined,
       };
     case 'file':
       return {