revert: roll back flatpak packaging experiment (#271 + follow-ups) (#297)

Reverts #271, #292, #293, #294, #295, #296.

The flatpak CI pipeline itself works end-to-end, but the installed bundle
surfaced three separate manifest issues during smoke-test on Wayland+NVIDIA:

1. GDK_BACKEND is not set, so without an X11 display in the sandbox GTK
   aborts with "Failed to initialize GTK".
2. libayatana-appindicator3 is not bundled in the GNOME 47 runtime, so
   libappindicator-sys panics the main thread.
3. The release binary is compiled via \`cargo build --release\` rather than
   \`cargo tauri build\`, so the \`custom-protocol\` feature is off and
   Tauri falls back to devUrl — the window opens but shows
   "Could not connect to localhost".

Rolling back so main stays on 1.43.0. A follow-up on the original PR
tracks the fixes needed before re-attempting.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/flatpak/dev.psysonic.Psysonic.yml

@@ -1,89 +0,0 @@
-app-id: dev.psysonic.Psysonic
-runtime: org.gnome.Platform
-runtime-version: '47'
-sdk: org.gnome.Sdk
-sdk-extensions:
-  - org.freedesktop.Sdk.Extension.rust-stable
-  - org.freedesktop.Sdk.Extension.node20
-command: psysonic
-separate-locales: false
-
-finish-args:
-  # Network: Subsonic server, Last.fm, Discord RPC, LRCLIB, Bandsintown
-  - --share=network
-  - --share=ipc
-  # Display
-  - --socket=wayland
-  - --socket=fallback-x11
-  # Audio: PulseAudio + ALSA, USB DACs (UMC202HD etc.)
-  - --socket=pulseaudio
-  - --device=all
-  # D-Bus: MPRIS, Discord RPC, tray icon
-  - --socket=session-bus
-  - --talk-name=org.mpris.MediaPlayer2.*
-  - --own-name=org.mpris.MediaPlayer2.psysonic
-  - --talk-name=com.discordapp.*
-  # Discord RPC unix socket lives in $XDG_RUNTIME_DIR
-  - --filesystem=xdg-run/discord-ipc-0:ro
-  - --filesystem=xdg-run/discord-ipc-1:ro
-  - --filesystem=xdg-run/discord-ipc-2:ro
-  - --filesystem=xdg-run/discord-ipc-3:ro
-  - --filesystem=xdg-run/discord-ipc-4:ro
-  # Tray icon (GNOME needs AppIndicator extension installed)
-  - --talk-name=org.kde.StatusNotifierWatcher
-  - --talk-name=org.freedesktop.Notifications
-  # Local music library (read-only, for future local-file playback)
-  - --filesystem=xdg-music:ro
-
-build-options:
-  append-path: /usr/lib/sdk/rust-stable/bin:/usr/lib/sdk/node20/bin
-  env:
-    - CARGO_HOME=/run/build/psysonic/cargo
-    - CARGO_NET_OFFLINE=true
-    - RUSTUP_TOOLCHAIN=stable
-
-modules:
-  - name: psysonic
-    buildsystem: simple
-    build-options:
-      env:
-        # Disables the in-app updater UI — Flathub owns updates for Flatpak installs
-        - VITE_PSYSONIC_FLATPAK=1
-        # Prevents tauri-build from checking whether the Vite dev server is running
-        - TAURI_SKIP_DEVSERVER_CHECK=true
-        # Last.fm API keys — replaced with real values by the CI job at build time
-        - VITE_LASTFM_API_KEY=__LASTFM_KEY__
-        - VITE_LASTFM_API_SECRET=__LASTFM_SECRET__
-        # npm offline cache — flatpak-node-generator places sources in flatpak-node/npm-cache
-        - npm_config_cache=/run/build/psysonic/flatpak-node/npm-cache
-    build-commands:
-      # Install npm dependencies from pre-generated offline sources
-      - npm ci --offline
-      # Build frontend (dist/ must exist before cargo compiles the Rust crate,
-      # because tauri-build embeds the assets at compile time)
-      - npm run build
-      # Build the Rust binary (offline, using pre-vendored cargo sources)
-      - cargo build --manifest-path src-tauri/Cargo.toml --release
-      # Install binary and assets
-      - install -Dm755 src-tauri/target/release/psysonic "${FLATPAK_DEST}/bin/psysonic"
-      - install -Dm644 dev.psysonic.Psysonic.desktop "${FLATPAK_DEST}/share/applications/dev.psysonic.Psysonic.desktop"
-      - install -Dm644 dev.psysonic.Psysonic.metainfo.xml "${FLATPAK_DEST}/share/metainfo/dev.psysonic.Psysonic.metainfo.xml"
-      - install -Dm644 src-tauri/icons/32x32.png "${FLATPAK_DEST}/share/icons/hicolor/32x32/apps/dev.psysonic.Psysonic.png"
-      - install -Dm644 src-tauri/icons/128x128.png "${FLATPAK_DEST}/share/icons/hicolor/128x128/apps/dev.psysonic.Psysonic.png"
-      - install -Dm644 src-tauri/icons/128x128@2x.png "${FLATPAK_DEST}/share/icons/hicolor/256x256/apps/dev.psysonic.Psysonic.png"
-      - install -Dm644 src-tauri/icons/icon.png "${FLATPAK_DEST}/share/icons/hicolor/512x512/apps/dev.psysonic.Psysonic.png"
-    sources:
-      - type: git
-        url: https://github.com/Psychotoxical/psysonic.git
-        # Updated automatically by the CI release job; bump manually for local builds
-        tag: app-v1.43.0
-        commit: PLACEHOLDER_COMMIT
-      # Generated by the CI job via flatpak-cargo-generator and flatpak-node-generator.
-      # Committed into git only for the Flathub mirror repo (separate from this source
-      # repo); locally, run packages/flatpak/generate-sources.sh to create them.
-      - cargo-sources.json
-      - npm-sources.json
-      - type: file
-        path: dev.psysonic.Psysonic.desktop
-      - type: file
-        path: dev.psysonic.Psysonic.metainfo.xml