73-video-thumbnails (#142)

This PR implements video thumbnails for `.mov`, `.webm`, and `.mp4` files in the `ContentLinkBlock` component.

Changes:
- Added the `poster` attribute to the `<video>` tag.
- Set the poster source to `{url}#t=1` to capture a clear preview frame at the 1-second mark.
- Verified locally that thumbnails are now correctly displayed instead of a black/empty box.

Closes #73

Reviewed-on: #142
Co-authored-by: Priyanshubhartistm <bhartipriyanshustm@gmail.com>
Co-committed-by: Priyanshubhartistm <bhartipriyanshustm@gmail.com>

src/app/core/state.ts

@@ -210,6 +210,8 @@ export const DEFAULT_PUBKEYS = import.meta.env.VITE_DEFAULT_PUBKEYS
 
 export const DUFFLEPUD_URL = "https://dufflepud.onrender.com"
 
+export const THUMBNAIL_URL = import.meta.env.VITE_THUMBNAIL_URL
+
 export const NIP46_PERMS =
   "nip44_encrypt,nip44_decrypt," +
   [