fix(jellyfin-api): use standard Authorization header

[fallenbagel]

Description

Replace X-Emby-Authorization with Authorization header to fix
authentication failures when users have <EnableLegacyAuthorization>false</EnableLegacyAuthorization> in their Jellyfin system.xml. This option was introduced in 10.11 (enabled by default) for testing without the legacy authorization methods and will be enforced (disabled by default) in 10.12. We should be using the modern authorization method anyway.

It is backwards compatible as the new header was introduced a while ago.

How Has This Been Tested?

• Authenticated against 10.11.x
• Authenticated against 10.10.x

Screenshots / Logs (if applicable)

Checklist:

• I have read and followed the contribution guidelines.
• Disclosed any use of AI (see our policy)
• I have updated the documentation accordingly.
• All new and existing tests passed.
• Successful build pnpm build
• Translation keys pnpm i18n:extract
• Database migration (if required)