Fullscreen player polish + Discord Rich Presence fixes (#1068)

* fix(fullscreen-player): drop track-number prefix from title, stop clipping descenders

The big title showed a zero-padded queue position ("11. ") before the
song name; remove it (the position still lives in the top bar). Also bump
line-height 1.05 -> 1.25 so overflow:hidden no longer crops descenders
(g, j, p, q, y) at 46px.

* feat(settings): clarify built-in Discord RP vs official Navidrome plugin

Add a bold notice atop the Discord Rich Presence block explaining it is
the built-in integration, and that users wanting the official Navidrome
Discord RP plugin should leave it off and enable "Show in Now Playing"
instead. Add a matching bold note to the Now Playing setting. New i18n
keys discordRichPresenceNotice / nowPlayingPluginNote across all 5 locales.

* fix(discord-rp): use HTTPS cover URL instead of local file:// path

Discord Rich Presence images are fetched by Discord's servers, so
large_image must be a key or an https:// URL they can reach. Since the
cover pipeline moved to an on-disk webp cache, coverArtUrlForDiscord
returned a file://.../800.webp path on cache hit, which Discord cannot
load and silently falls back to the app icon. Always hand it the
getCoverArt URL; MPRIS keeps the local file:// path unchanged.

* i18n(settings): fill discordRichPresenceNotice + nowPlayingPluginNote for es, nb, ro, ru

The two new Discord-RP notice keys had only landed in 5 of the 9 locales;
complete the set so no locale falls back to English.

* docs(changelog): fullscreen title + Discord RP fixes (PR #1068)

src/locales/en/settings.ts

@@ -228,6 +228,7 @@ export const settings = {
   preloadMiniPlayerDesc: 'Build the mini player window in the background at app start so it shows content instantly on first open. Uses a little extra memory.',
   discordRichPresence: 'Discord Rich Presence',
   discordRichPresenceDesc: 'Show the currently playing track on your Discord profile. Requires Discord to be running.',
+  discordRichPresenceNotice: 'Heads up: this is Psysonic\'s built-in Discord Rich Presence. If you\'d rather use the official Navidrome Discord Rich Presence plugin, leave this switched off and enable "Show in Now Playing" further down this page instead.',
   useCustomTitlebar: 'Custom title bar',
   useCustomTitlebarDesc: 'Replace the system title bar with a built-in one that matches the app theme. Disable to use the native GNOME/GTK title bar.',
   linuxWebkitSmoothScroll: 'Smooth wheel (Linux)',
@@ -255,6 +256,7 @@ export const settings = {
   discordTemplateName: 'User list line (name)',
   nowPlayingEnabled: 'Show in Now Playing',
   nowPlayingEnabledDesc: 'Broadcast your currently playing track to the server\'s live listener view. Disable to stop sending playback data.',
+  nowPlayingPluginNote: 'Required when using the official Navidrome Discord Rich Presence plugin.',
   enableBandsintown: 'Bandsintown tour dates',
   enableBandsintownDesc: 'Show upcoming concerts for the current artist in the Info tab. Data is fetched from the public Bandsintown API.',
   lyricsServerFirst: 'Prefer server lyrics',