fix(mainstage): rename Home Page setting, start-page fallback + empty state (#975)

* fix(mainstage): rename Home Page setting, add start-page fallback + empty state

- Rename "Home Page" personalisation section to "Mainstage" across 9 locales
  so the heading matches the sidebar entry; add "mainstage" search keyword.
- Index route "/" now redirects to the first visible library item when the
  Mainstage sidebar entry is hidden, instead of stranding the app on a blank
  page. New pure resolveStartRoute() mirrors sidebar order + nav-mode gating.
- Show a guided empty state on Mainstage when every section is toggled off,
  with a CTA into Settings -> Personalisation.
- Unit tests for resolveStartRoute.

* docs(changelog): Mainstage rename, start-page fallback + empty state (#975)

CHANGELOG.md

@@ -411,6 +411,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 
+### Mainstage — renamed to match the sidebar
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), reported by zunoz on Discord, PR [#975](https://github.com/Psychotoxical/psysonic/pull/975)**
+
+* The **Settings → Personalisation** section for customising the home page is renamed **Mainstage** so it matches the sidebar entry it controls. Localised across all 9 languages; settings search still finds it under the new name.
+
+
+
 
 ## Fixed
 
@@ -840,6 +848,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * The queue collapse handle now shows a hand cursor like every other button; the thin resize line beside it keeps the resize cursor.
 * On Favorites, the **Plays**, **Last Played** and **BPM** columns are now actually sortable — they showed a clickable cursor but clicking did nothing.
 
+### Mainstage — no more blank start page
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), reported by zunoz on Discord, PR [#975](https://github.com/Psychotoxical/psysonic/pull/975)**
+
+* Hiding **Mainstage** from the sidebar no longer leaves the app opening on a blank page — it now starts on the first visible library entry instead.
+* When every Mainstage section is turned off, the page shows a short message with a shortcut into **Settings → Personalisation** rather than appearing empty.
+
 ## [1.46.0] - 2026-05-18
 
 > **🙏 Special thanks to [@zz5zz](https://github.com/zz5zz)** for his tireless quirk-spotting and bug reports on the [Psysonic Discord](https://discord.gg/AMnDRErm4u) — several of the polish fixes in this release landed directly off the back of his messages.