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)

CHANGELOG.md

@@ -191,6 +191,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Fixed
 
+### Fullscreen player — title cleanup
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#1068](https://github.com/Psychotoxical/psysonic/pull/1068)**
+
+* The song title no longer shows a leading track number, and letters with descenders (g, j, p, q, y) are no longer clipped along the bottom edge.
+
+### Discord Rich Presence — album art and clearer settings
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#1068](https://github.com/Psychotoxical/psysonic/pull/1068)**
+
+* Album art shows again when the cover source is "Server (via album info)" — Discord was handed a local file path it cannot fetch and fell back to the app icon; it now receives a reachable image URL.
+* **Settings → Integrations:** added notices clarifying that this is the built-in Discord Rich Presence, and that the official Navidrome Discord RP plugin needs "Show in Now Playing" enabled instead.
+
 ### Local index — multi-genre browse, filters, and counts
 
 **By [@cucadmuh](https://github.com/cucadmuh), reported by HiveMind on the Psysonic Discord, PR [#1059](https://github.com/Psychotoxical/psysonic/pull/1059)**