chore: v0.5.3 — bump version + CHANGELOG entry

Final headline-feature release. Per David: 'this app is kinda done'
once Quick Stations picker + history export ship. After this version,
polish remains but no headline features are missing.

Bundled with v0.5.0's eventual Web Store upload — when v0.5.0
clears re-review, we'll build a v0.5.3 ZIP directly from main and
upload that as the next user-visible update. Users at v0.4.0 jump
straight to v0.5.3, getting all the polish in one notification.

manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "RangerHQ Tuner",
-  "version": "0.5.2",
+  "version": "0.5.3",
   "description": "Lightweight SomaFM radio player. Logs what plays. One-click search to Spotify, YouTube, Apple Music, Bandcamp. No telemetry.",
   "author": "David Keane",
   "homepage_url": "https://davidtkeane.com/rangerhq-tuner",