fix(cover): embed fanart.tv project key so from-source builds work (#1139)

The project key was injected only at our build time (CI secret / option_env!),
so AUR, Nix and any from-source build had no key baked in and the External
Artwork toggle was inert there. Commit it as a source literal (like the Last.fm
key, and as fanart.tv terms expect: the app ships a project key, users add
their own on top via BYOK). Drops the now-redundant CI wiring.

src-tauri/src/cover_cache/external.rs

@@ -15,6 +15,13 @@ use super::fetch::build_subsonic_url;
 
 const FANART_API_BASE: &str = "https://webservice.fanart.tv/v3/music";
 const MUSICBRAINZ_BASE: &str = "https://musicbrainz.org/ws/2";
+/// fanart.tv project `api_key`, embedded in the binary like Last.fm's key and as
+/// fanart.tv's own terms expect ("sent in addition to your project key" — the app
+/// ships a project key, users add a personal one on top). Committed as a literal
+/// (not a build secret) so every build — CI, local, AUR, Nix, from-source — has
+/// it; desktop-app keys are extractable from any binary anyway. Users can still
+/// add their own personal key (BYOK, §22), sent in addition to this one.
+pub(super) const FANART_PROJECT_KEY: &str = "a32e00543d18deadb797bc0cc9826760";
 /// MusicBrainz requires a meaningful, contactable User-Agent (their ToS).
 const MUSICBRAINZ_USER_AGENT: &str = concat!(
     "Psysonic/",

src-tauri/src/cover_cache/external_ensure.rs

@@ -188,13 +188,14 @@ pub(super) async fn try_external_fanart(
     requested: u32,
     surface: &str,
 ) -> Option<PathBuf> {
-    // Behind the project key: a runtime env var (dev convenience) wins, else the
-    // key baked in at build time via `option_env!` (release builds). No secret
-    // lands in the repo. The BYOK personal key is optional (§22).
+    // Project key: a runtime env var (dev convenience) wins, else the embedded
+    // `FANART_PROJECT_KEY` committed in the source — so the feature works in every
+    // build (CI, local, AUR, Nix, from-source), not just ones built with a secret.
+    // The BYOK personal key is optional and sent in addition (§22).
     let api_key = std::env::var("PSYSONIC_FANART_KEY")
         .ok()
-        .or_else(|| option_env!("PSYSONIC_FANART_KEY").map(str::to_string))
-        .filter(|k| !k.is_empty())?;
+        .filter(|k| !k.is_empty())
+        .unwrap_or_else(|| external::FANART_PROJECT_KEY.to_string());
     // BYOK personal key (§22): the settings field wins, else the dev env var.
     let byok = args
         .external_artwork_byok

src-tauri/src/cover_cache/mod.rs

@@ -135,9 +135,9 @@ pub struct CoverCacheEnsureArgs {
     /// with the album/artist name. On-demand UI ensures leave it `None`.
     #[serde(default)]
     pub library_server_id: Option<String>,
-    /// Image-scraper spike (§16 P0): when true, an artist `fanart` ensure may
-    /// fetch a fanart.tv background into `{tier}-fanart.webp`. Inert unless the
-    /// fanart project key is present (`PSYSONIC_FANART_KEY`). Off by default.
+    /// External artwork (§16): when true, an artist `fanart`/`banner` ensure may
+    /// fetch from fanart.tv into `{tier}-{provider}.webp`. Gated by the master
+    /// toggle (off by default); the project key is embedded (`FANART_PROJECT_KEY`).
     #[serde(default)]
     pub external_artwork_enabled: bool,
     /// Surface intent for external artwork — `fanart` for the 16:9 artist