perf: drastically reduce background API requests to Navidrome (v1.34.5)

- NowPlaying polling: only active while dropdown is open + respects
  Page Visibility API — was firing every 10s unconditionally (~8.6k req/day)
- Connection check interval: 30s → 120s (4× reduction)
- Queue sync debounce: 1.5s → 5s (prevents burst on rapid skip)
- Rating prefetch: add 7-minute in-memory TTL cache for artist/album
  ratings — repeated random album loads no longer re-fetch known ratings

Fixes server log flooding reported by users behind reverse proxies (Traefik).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/Cargo.lock

@@ -3339,7 +3339,7 @@ dependencies = [
 
 [[package]]
 name = "psysonic"
-version = "1.34.4"
+version = "1.34.5"
 dependencies = [
  "biquad",
  "discord-rich-presence",

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "psysonic"
-version = "1.34.4"
+version = "1.34.5"
 description = "Psysonic Desktop Music Player"
 authors = []
 license = ""

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Psysonic",
-  "version": "1.34.4",
+  "version": "1.34.5",
   "identifier": "dev.psysonic.player",
   "build": {
     "beforeDevCommand": "npm run dev",