build(wails): add the v3 toolchain alongside v2

Phase 1 of plan 009. The app still builds and runs on v2 — nothing in
main.go or backend/ has moved yet — but the v3 CLI, its pinned runtime
and its build-asset tree are now present, which is what Phase 2 needs.

- wails/v3 v3.0.0-beta.8 pinned per D5, and wails3 added to the `tool`
  block beside the v2 CLI per D3. Both are vendored; neither is a
  global install.
- build/ now holds the v3 build assets, copied wholesale from a
  `wails3 init` scaffold rather than hand-written. That collides with
  this repo's existing use of build/ as ignored build *output*, so
  .gitignore narrows to build/bin/ and bin/ and the assets are tracked.
  The mobile platforms are not carried: this is a desktop player
  (MPRIS over D-Bus, beep, XDG paths) and cannot target them.
- build/config.yml's info block is filled from wails.json, which stays
  for now because the v2 CLI still reads it.
- Taskfile.yml defaults PACKAGE_MANAGER to pnpm, since the scaffold
  assumes npm and frontend/package.json.md5 is part of the dep-caching
  scheme.

One deviation from the plan worth recording. webkitgtk-6.0 is not
installed on this machine, so the default GTK4 path is unavailable and
the gtk3 fallback is in use. That also means `go tool wails3` does not
work — the CLI itself fails to compile without webkitgtk-6.0 — while
`go run -tags gtk3 .../cmd/wails3` does. The Makefile rewrite in the
next commit has to account for that, and it goes away once the GTK4
dependency is installed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UDCbcCZQepnpSQYJ6SxxZm

build/linux/nfpm/nfpm.yaml

@@ -0,0 +1,80 @@
+# Feel free to remove those if you don't want/need to use them.
+# Make sure to check the documentation at https://nfpm.goreleaser.com
+#
+# The lines below are called `modelines`. See `:help modeline`
+
+name: "yjref"
+arch: ${GOARCH}
+platform: "linux"
+version: "0.1.0"
+section: "default"
+priority: "extra"
+maintainer: ${GIT_COMMITTER_NAME} <${GIT_COMMITTER_EMAIL}>
+description: "A yjref application"
+vendor: "My Company"
+homepage: "https://wails.io"
+license: "MIT"
+release: "1"
+
+contents:
+  - src: "./bin/yjref"
+    dst: "/usr/local/bin/yjref"
+  - src: "./build/appicon.png"
+    dst: "/usr/share/icons/hicolor/128x128/apps/yjref.png"
+  - src: "./build/linux/yjref.desktop"
+    dst: "/usr/share/applications/yjref.desktop"
+
+# Default dependencies for the GTK4 + WebKitGTK 6.0 stack (Ubuntu 24.04+ / Debian 13+)
+depends:
+  - libgtk-4-1
+  - libwebkitgtk-6.0-4
+
+# Distribution-specific overrides for different package formats
+overrides:
+  # RPM packages for Fedora / RHEL / AlmaLinux / Rocky Linux
+  rpm:
+    depends:
+      - gtk4
+      - webkitgtk6.0
+
+  # Arch Linux packages
+  archlinux:
+    depends:
+      - gtk4
+      - webkitgtk-6.0
+
+# scripts section to ensure desktop database is updated after install
+scripts:
+  postinstall: "./build/linux/nfpm/scripts/postinstall.sh"
+  # You can also add preremove, postremove if needed
+  # preremove: "./build/linux/nfpm/scripts/preremove.sh"
+  # postremove: "./build/linux/nfpm/scripts/postremove.sh"
+
+# If you build your app with -tags gtk3 (legacy WebKit2GTK 4.1 stack — supported through v3.0.x, removed in v3.1),
+# replace the depends/overrides above with these:
+#
+# depends:
+#   - libgtk-3-0
+#   - libwebkit2gtk-4.1-0
+# overrides:
+#   rpm:
+#     depends:
+#       - gtk3
+#       - webkit2gtk4.1
+#   archlinux:
+#     depends:
+#       - gtk3
+#       - webkit2gtk-4.1
+#
+# replaces:
+#   - foobar
+# provides:
+#   - bar
+# recommends:
+#   - whatever
+# suggests:
+#   - something-else
+# conflicts:
+#   - not-foo
+#   - not-bar
+# changelog: "changelog.yaml"

build/linux/nfpm/scripts/postinstall.sh

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+# Update desktop database for .desktop file changes
+# This makes the application appear in application menus and registers its capabilities.
+if command -v update-desktop-database >/dev/null 2>&1; then
+  echo "Updating desktop database..."
+  update-desktop-database -q /usr/share/applications
+else
+  echo "Warning: update-desktop-database command not found. Desktop file may not be immediately recognized." >&2
+fi
+
+# Update MIME database for custom URL schemes (x-scheme-handler)
+# This ensures the system knows how to handle your custom protocols.
+if command -v update-mime-database >/dev/null 2>&1; then
+  echo "Updating MIME database..."
+  update-mime-database -n /usr/share/mime
+else
+  echo "Warning: update-mime-database command not found. Custom URL schemes may not be immediately recognized." >&2
+fi
+
+exit 0

build/linux/nfpm/scripts/postremove.sh

@@ -0,0 +1 @@
+#!/bin/bash

build/linux/nfpm/scripts/preinstall.sh

@@ -0,0 +1 @@
+#!/bin/bash

build/linux/nfpm/scripts/preremove.sh

@@ -0,0 +1 @@
+#!/bin/bash