feat(core,fuse,gui): Proton theme, photos on the map and an opt-in street map

- The Proton accent preference becomes a whole Proton theme that also
  holds against a GTK theme imported from gtk.css; folders get Proton's
  purple folder icon while it is on.
- Places map markers show one of each town's photos with a count, and
  zoomed in on a town every photo sits where it was taken
  (Request::PlaceLocations). Photos taken on one spot are listed in a
  popover. "Show on map" in the photo viewer goes to the Places map.
- The built-in map draws country borders, sea and land in their own
  colours.
- An opt-in street map from OpenFreeMap (vector tiles drawn with cairo,
  cached on disk up to 256 MB), with the OpenStreetMap credit on the map
  and in About.
- Translations for all catalogs; changelog folded into 2.3.0.

crates/pdfs-gui/resources/icons/scalable/places/pdfs-proton-folder.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="48" height="48" viewBox="0 0 48 48">
+  <path fill="#6d4aff" d="M4 12a4 4 0 0 1 4-4h11.2a4 4 0 0 1 2.9 1.2L25 12h15a4 4 0 0 1 4 4v22a4 4 0 0 1-4 4H8a4 4 0 0 1-4-4z"/>
+  <path fill="#8a6eff" d="M4 19a3 3 0 0 1 3-3h34a3 3 0 0 1 3 3v19a4 4 0 0 1-4 4H8a4 4 0 0 1-4-4z"/>
+  <path fill="#ffffff" fill-opacity="0.18" d="M7 16h34a3 3 0 0 1 3 3v1a3 3 0 0 0-3-3H7a3 3 0 0 0-3 3v-1a3 3 0 0 1 3-3z"/>
+</svg>

crates/pdfs-gui/resources/pdfs.gresource.xml

@@ -10,14 +10,18 @@
     <file preprocess="xml-stripblanks">scalable/actions/pdfs-filter-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/actions/pdfs-offline-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/actions/pdfs-online-only-symbolic.svg</file>
+    <!-- The Proton theme's folder: a full-colour icon from the icon theme
+         can't be recoloured by CSS. -->
+    <file preprocess="xml-stripblanks">scalable/places/pdfs-proton-folder.svg</file>
     <!-- The app icon, from the one file packaging installs, so the in-app brand
          matches the launcher and resolves even when nothing is installed. -->
     <file alias="scalable/apps/io.narl.proton-drive-linux.svg" preprocess="xml-stripblanks">../../../packaging/io.narl.proton-drive-linux.svg</file>
   </gresource>
   <!-- The app stylesheet, loaded once at startup. Colours come from the
        libadwaita palette so the app follows the system accent, light/dark and
-       high contrast; the Proton purple accent is a separate, opt-in provider. -->
+       high contrast. The Proton theme is a separate, opt-in provider. -->
   <gresource prefix="/de/nils/protondrivelinux">
     <file>style.css</file>
+    <file>proton-theme.css</file>
   </gresource>
 </gresources>

crates/pdfs-gui/resources/proton-theme.css

@@ -0,0 +1,72 @@
+/* Proton theme — the Proton web apps' Snow (light) and Carbon (dark) palettes.
+ *
+ * Loaded by main.rs after libadwaita's own stylesheet, which it re-applies on
+ * top of the user's GTK theme so that theme's hard-coded colours can't show
+ * through. Only libadwaita's colour variables are set here; every widget
+ * derives its look from them. Values from ProtonMail/WebClients,
+ * packages/colors/themes/src/{snow,carbon}/standard-base.css.
+ */
+
+:root {
+    --accent-bg-color: #6d4aff;
+    --accent-fg-color: #ffffff;
+    --destructive-bg-color: #dc3251;
+    --destructive-fg-color: #ffffff;
+    --error-bg-color: #dc3251;
+    --error-fg-color: #ffffff;
+    --success-bg-color: #1ea885;
+    --success-fg-color: #ffffff;
+    --warning-bg-color: #ff9900;
+    --warning-fg-color: rgb(0 0 0 / 80%);
+
+    --window-bg-color: #ffffff;
+    --window-fg-color: #0c0c14;
+    --view-bg-color: #ffffff;
+    --view-fg-color: #0c0c14;
+    --headerbar-bg-color: #ffffff;
+    --headerbar-fg-color: #0c0c14;
+    --headerbar-backdrop-color: #ffffff;
+    --sidebar-bg-color: #f5f4f2;
+    --sidebar-fg-color: #0c0c14;
+    --sidebar-backdrop-color: #f8f8f6;
+    --secondary-sidebar-bg-color: #f8f8f6;
+    --secondary-sidebar-fg-color: #0c0c14;
+    --secondary-sidebar-backdrop-color: #f8f8f6;
+    --card-bg-color: #f5f4f2;
+    --card-fg-color: #0c0c14;
+    --dialog-bg-color: #ffffff;
+    --dialog-fg-color: #0c0c14;
+    --popover-bg-color: #ffffff;
+    --popover-fg-color: #0c0c14;
+    --thumbnail-bg-color: #f5f4f2;
+    --thumbnail-fg-color: #0c0c14;
+}
+
+@media (prefers-color-scheme: dark) {
+    :root {
+        --destructive-bg-color: #f5385a;
+        --error-bg-color: #f5385a;
+
+        --window-bg-color: #1e1c26;
+        --window-fg-color: #ffffff;
+        --view-bg-color: #1e1c26;
+        --view-fg-color: #ffffff;
+        --headerbar-bg-color: #1e1c26;
+        --headerbar-fg-color: #ffffff;
+        --headerbar-backdrop-color: #1e1c26;
+        --sidebar-bg-color: #16141c;
+        --sidebar-fg-color: #ffffff;
+        --sidebar-backdrop-color: #16141c;
+        --secondary-sidebar-bg-color: #1a1821;
+        --secondary-sidebar-fg-color: #ffffff;
+        --secondary-sidebar-backdrop-color: #1a1821;
+        --card-bg-color: #292733;
+        --card-fg-color: #ffffff;
+        --dialog-bg-color: #292733;
+        --dialog-fg-color: #ffffff;
+        --popover-bg-color: #292733;
+        --popover-fg-color: #ffffff;
+        --thumbnail-bg-color: #292733;
+        --thumbnail-fg-color: #ffffff;
+    }
+}

crates/pdfs-gui/resources/style.css

@@ -4,7 +4,8 @@
  * var(--success-color), ...) so the app follows the system accent, light/dark
  * and high contrast. The one exception is the photo viewer, which always sits
  * on a near-black backdrop and so uses fixed light-on-dark colours. The Proton
- * purple accent is opt-in and lives in its own provider (see main.rs).
+ * theme is opt-in and lives in its own provider (see main.rs and
+ * proton-theme.css).
  */
 
 /* Brand */
@@ -89,7 +90,11 @@ progressbar.browser-status-meter trough, progressbar.browser-status-meter progre
 
 /* Photos: how many timeline filters are on, as a small badge on the Filters button. */
 .filter-count { min-width: 18px; padding: 0 5px; border-radius: 999px; font-size: 0.8em; font-weight: 700; color: var(--accent-fg-color); background-color: var(--accent-bg-color); }
-/* The Places map: water a faint wash of the text colour, bubbles (drawn in
- * the area's own colour) in the accent. */
-.places-map-frame { border-radius: 12px; background: color-mix(in srgb, currentColor 5%, transparent); }
+/* The Places map: sea and land come in the map's own colours; markers (drawn
+ * in the area's own colour) in the accent. */
+.places-map-frame { border-radius: 12px; }
 .places-map { color: var(--accent-bg-color); }
+/* Credit on the Places street map, in the corner as on every web map. */
+.places-spot-photo { padding: 0; }
+.places-spot-photo picture { border-radius: 6px; overflow: hidden; }
+.places-map-credit { padding: 2px 8px; border-top-left-radius: 8px; color: var(--window-fg-color); background: color-mix(in srgb, var(--window-bg-color) 80%, transparent); }