feat(gui): polish pass over wording, icons and responsiveness

The Sync page gives each folder one card with its state, a Synced /
Online only switch and a menu for the rest; switching either way asks
first and the download prompt shows the free space on the disk.

Enabling, disabling and restarting the Proton Drive service ran
systemctl on GTK's main thread and froze the window. They now run in
the background, and every Retry button goes through one shared restart
helper.

Ten icons are bundled under resources/icons for glyphs no stock theme
has or that read ambiguously (sync, share, people, link, menu, map and
so on). A new test fails when the app or search prompt asks for a
symbolic icon that is neither bundled nor on a list checked against
Adwaita 50, libadwaita and GTK, or when a bundled icon is missing from
the resource manifest. The tray's sync icon, which Adwaita 50 no longer
ships, is now view-refresh.

Wording follows one glossary, recorded in docs/TRANSLATING.md: "Proton
Drive service" instead of "mount service" or "daemon", "Online only"
instead of "On-demand", "Proton Drive folder" instead of "mountpoint".
Dialog headings and buttons use title case and page titles match the
sidebar. Dates go through one formatter (app/dates.rs) and sizes
through i18n::human_bytes, and the cache label is translated.

The status tick stops while the window is hidden or minimized and runs
every fifth tick while it is unfocused, refreshing as soon as it gains
focus. "Sync complete" is announced only for large batches and only
when the window isn't focused. Smaller fixes: Empty Trash hides when
there is nothing to empty, copy buttons confirm with a check mark, the
sidebar status spins until the first report, and Photos moves Import
and Find Duplicates into a menu beside a labelled Select toggle.

All catalogs are updated and complete.

crates/pdfs-gui/tests/icon_names.rs

@@ -0,0 +1,160 @@
+//! Every symbolic icon the app window and the search prompt ask for must
+//! exist on a stock GNOME desktop.
+//!
+//! An icon name that no theme ships shows up as a missing-image glyph, and
+//! nothing fails until someone looks. So each `"…-symbolic"` literal in the
+//! sources has to be either one of the `pdfs-*` icons bundled in
+//! `resources/icons` (and listed in the gresource manifest), or on
+//! [`STOCK`], a list of names checked against Adwaita 50, libadwaita and
+//! GTK's own built-in icons.
+//!
+//! The tray is left out: its icons are drawn by the panel, from the panel's
+//! theme, not from our resources.
+
+use std::collections::BTreeSet;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+/// Stock symbolic icons the app may use. Before adding a name, check that
+/// Adwaita has it outside its `legacy` folder, or that libadwaita or GTK
+/// ship it themselves.
+const STOCK: &[&str] = &[
+    // libadwaita
+    "adw-external-link-symbolic",
+    // GTK's built-in icons
+    "info-outline-symbolic",
+    // Adwaita
+    "checkbox-checked-symbolic",
+    "checkbox-symbolic",
+    "computer-symbolic",
+    "dialog-error-symbolic",
+    "dialog-warning-symbolic",
+    "document-edit-symbolic",
+    "document-open-recent-symbolic",
+    "document-open-symbolic",
+    "document-save-symbolic",
+    "drive-harddisk-symbolic",
+    "edit-copy-symbolic",
+    "edit-delete-symbolic",
+    "edit-find-symbolic",
+    "edit-undo-symbolic",
+    "folder-download-symbolic",
+    "folder-new-symbolic",
+    "folder-open-symbolic",
+    "folder-remote-symbolic",
+    "folder-symbolic",
+    "go-down-symbolic",
+    "go-jump-symbolic",
+    "go-next-symbolic",
+    "go-previous-symbolic",
+    "go-up-symbolic",
+    "image-missing-symbolic",
+    "image-x-generic-symbolic",
+    "list-add-symbolic",
+    "mark-location-symbolic",
+    "media-playback-pause-symbolic",
+    "media-playback-start-symbolic",
+    "network-idle-symbolic",
+    "network-offline-symbolic",
+    "non-starred-symbolic",
+    "object-select-symbolic",
+    "preferences-system-symbolic",
+    "process-stop-symbolic",
+    "starred-symbolic",
+    "system-search-symbolic",
+    "text-x-generic-symbolic",
+    "user-trash-symbolic",
+    "view-grid-symbolic",
+    "view-list-symbolic",
+    "view-more-symbolic",
+    "view-paged-symbolic",
+    "view-pin-symbolic",
+    "view-refresh-symbolic",
+    "window-close-symbolic",
+    "zoom-fit-best-symbolic",
+    "zoom-in-symbolic",
+    "zoom-out-symbolic",
+];
+
+fn crate_dir() -> PathBuf {
+    PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+}
+
+fn rust_files(dir: &Path, out: &mut Vec<PathBuf>) {
+    for entry in fs::read_dir(dir).unwrap() {
+        let path = entry.unwrap().path();
+        if path.is_dir() {
+            rust_files(&path, out);
+        } else if path.extension().is_some_and(|e| e == "rs") {
+            out.push(path);
+        }
+    }
+}
+
+/// Every `"name-symbolic"` string literal in `source`. Found by suffix rather
+/// than by pairing quotes, so an escaped quote or a `'"'` elsewhere in the
+/// file can't hide one.
+fn symbolic_literals(source: &str) -> Vec<String> {
+    const SUFFIX: &str = "-symbolic\"";
+    let is_name = |c: char| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-';
+    source
+        .match_indices(SUFFIX)
+        .filter_map(|(at, _)| {
+            let head = &source[..at];
+            let start = head.trim_end_matches(is_name).len();
+            (start > 0 && head[..start].ends_with('"'))
+                .then(|| format!("{}-symbolic", &head[start..]))
+        })
+        .collect()
+}
+
+/// The `pdfs-*` icons in `resources/icons`, by name.
+fn bundled() -> BTreeSet<String> {
+    let mut names = BTreeSet::new();
+    let root = crate_dir().join("resources/icons/scalable");
+    for context in fs::read_dir(root).unwrap() {
+        for icon in fs::read_dir(context.unwrap().path()).unwrap() {
+            let path = icon.unwrap().path();
+            if let Some(name) = path.file_stem().and_then(|s| s.to_str()) {
+                names.insert(name.to_string());
+            }
+        }
+    }
+    names
+}
+
+#[test]
+fn every_symbolic_icon_exists_on_a_stock_desktop() {
+    let mut files = vec![crate_dir().join("src/prompt.rs")];
+    rust_files(&crate_dir().join("src/app"), &mut files);
+    let bundled = bundled();
+    let mut unknown = BTreeSet::new();
+    for file in files {
+        let source = fs::read_to_string(&file).unwrap();
+        for name in symbolic_literals(&source) {
+            if !bundled.contains(&name) && !STOCK.contains(&name.as_str()) {
+                let file = file
+                    .strip_prefix(crate_dir())
+                    .unwrap()
+                    .display()
+                    .to_string();
+                unknown.insert(format!("{name} ({file})"));
+            }
+        }
+    }
+    assert!(
+        unknown.is_empty(),
+        "icons that are neither bundled nor on the stock list:\n  {}",
+        unknown.into_iter().collect::<Vec<_>>().join("\n  ")
+    );
+}
+
+#[test]
+fn every_bundled_icon_is_in_the_resource_manifest() {
+    let manifest = fs::read_to_string(crate_dir().join("resources/pdfs.gresource.xml")).unwrap();
+    let missing: Vec<String> = bundled()
+        .into_iter()
+        .filter(|name| name.starts_with("pdfs-") && !manifest.contains(&format!("/{name}.svg<")))
+        .collect();
+    assert!(missing.is_empty(), "not in pdfs.gresource.xml: {missing:?}");
+}