fix: show 'Title - Language' in subtitle/audio track selector (matches Jellyfin style)

[mr-brune]

Problem

When multiple subtitle (or audio) tracks share the same title field in an MKV file — a common occurrence with Crunchyroll/Erai-raws releases where all tracks are titled CR — the track selector shows identical, indistinguishable entries.

Root Cause

In app/src/view/player_setting.cpp, the track label was built as:

std::string title = mpv.getString(fmt::format("track-list/{}/title", n));
if (title.empty()) title = mpv.getString(fmt::format("track-list/{}/lang", n));
if (title.empty()) title = fmt::format("{} track {}", type, n);

The lang field was only used as a fallback when title was empty. When title was non-empty but identical across all tracks (e.g. CR), the language was never shown.

Fix

Added a langCodeToName() helper that maps ISO 639-1 (2-letter) and ISO 639-2 (3-letter) codes to full English language names, then builds the label as "Title - Language" — mirroring exactly how Jellyfin displays track selection:

std::string langName = langCodeToName(lang);
if (!title.empty() && !langName.empty())
    title = fmt::format("{} - {}", title, langName);  // "CR - English"

Result

With a real-world MKV file (Saga of Tanya the Evil S02E03, Erai-raws/Crunchyroll):

Before	After
CR	CR - English
Brazilian_CR	Brazilian_CR - Portuguese
Latin_America_CR	Latin_America_CR - Spanish
CR	CR - Spanish
CR	CR - Arabic
CR	CR - French
CR	CR - German
CR	CR - Italian
CR	CR - Russian

This applies to both subtitle and audio tracks.