fix #1582: Missing Poster attribute on Video Element

[rjmoggach]

Description:

Fix poster attribute only being set when nativeControls is enabled. The poster was incorrectly conditional on nativeControls in both the core provider element and React provider, causing poster images to not display when using custom video controls.

Changes:

• Remove nativeControls condition from poster attribute in provider-element.ts
• Remove nativeControls condition from poster attribute in React provider.tsx

Fixes poster display for video players using custom controls instead of native browser controls.

Summary of Changes Made:

Fixed Files:

1. /packages/vidstack/src/elements/define/provider-element.ts - Line 121 (but this wasn't the actual issue for React apps)
2. /packages/react/src/components/provider.tsx - Line 171 (this was the real fix for react)

Ready?

Tried it with buck bunny and seems to work.