refactor(server): share Jellyfin/Emby API implementations via ServerDialect

[MathiasDevelopes]

The Jellyfin and Emby API implementations were ~90% copy-pasted (~1,900 duplicated lines across 24 files). Both servers speak the same API with small, enumerable differences.

Behavior unifications (previously drifted copies):

• 5-min caches for user views and display preferences now apply to Jellyfin too (Emby already had them).
• Ancestors and special-features lookups fail gracefully on both.
• Jellyfin image/playback URLs resolve baseUrl lazily, fixing stale URLs after a server URL change.
• Image query params are URL-encoded on both servers.
• Emby now logs network requests/responses/errors like Jellyfin already did (shared attachServerInterceptors).

Tests: twin playback/live_tv test pairs merged into server_core, plus a new dialect test pinning per-server paths and capability gates.

Pull Request

Summary

This PR deduplicates Jellyfin/Emby API logic, by consolidating common logic and storing the differences in a ServerDialect class.

AI Assistance

Refactor plan and implementation were generated by Kimi K3 (Moonshot AI).
I spot-checked key files rather than reviewing the full diff line-by-line,
and tested the build against a Jellyfin and Emby server (see Test Steps).

Type of Change

• Bug fix
• New feature
• Refactor
• Performance improvement
• UI/UX update
• Documentation update
• Build/CI change
• Other (describe):

Changes Made

• Add ServerDialect capturing auth scheme, user-scoped vs user-less endpoint paths, capability flags (QuickConnect, lyrics, media segments, remote subtitle search), api_key image auth and the per-server display-preferences client name.
• Move the 12 duplicated API implementations into server_core as dialect-parameterized Server*Api classes.
• Extract shared interceptor wiring (auth header, redirects, network logging) into attachServerInterceptors.
• Both media server clients are now thin wiring shells; package names and client classes unchanged, so app code is untouched.

Platform

• Android
• iOS
• tvOS
• Web
• macOS
• Windows
• Linux
• All / Shared code

Testing

Describe how this change was tested.

• Tested on emulator / simulator
• Tested on physical device
• Manual testing completed
• Not tested (explain why):

Test Steps

Tested Linux build against Jellyfin and Emby server, verified that login, library browsing, playback, favorites, and resume working.

Checklist

• Code builds successfully
• Code follows project style and conventions
• No unnecessary commented-out code
• No new warnings introduced

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