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.

docs/TRANSLATING.md

@@ -63,6 +63,19 @@ stored as `language` in `config.json` and takes effect the next time they start.
 - Keep product names as they are: Proton Drive, Proton, Google Takeout.
 - Use the same term for the same thing across the catalog, and follow the terminology of your
   desktop (GNOME or KDE) for common actions such as Trash, Preferences and Cancel.
+- The English UI uses one term per concept. Pick one translation for each and keep it:
+
+  | Concept | English term |
+  |---|---|
+  | The root of the user's Drive | My files |
+  | The background service | Proton Drive service (never "daemon" or "mount") |
+  | A folder with a full copy on this computer | Synced folder |
+  | A folder whose files download when opened | Online-only folder |
+  | A single file kept on this computer | Available offline |
+  | A single file that is not on this computer | Online only |
+  | Where My files appears on disk | Proton Drive folder |
+  | Stop syncing a folder | Stop syncing |
+  | Two versions of one file | Conflict |
 
 ## Rules for developers
 

docs/UI_UX_PLAN.md

@@ -283,7 +283,8 @@ Header: `[‹ ›]  Path bar (breadcrumbs, scroll to end, Ctrl+L to edit)  … [
 | Cloud-only file | Online only | none / `cloud-outline` |
 | Pinned file | Available offline | pin/download-filled custom icon, not stars |
 | Upload | Upload files / Upload folder | `document-upload`-style arrow up, custom pair |
-| Folder sync mode | Synced / On-demand | — |
+| Folder sync mode | Synced / Online only | — |
+| Where My files appears on disk | Proton Drive folder — never "mountpoint" in UI | — |
 | Stop syncing a folder | Stop syncing… | `media-playback-stop-symbolic` in a menu, not trash |
 | Remove a computer | Remove computer… | destructive, in menu |
 | Conflict copy | Conflict | `dialog-warning-symbolic` + warning colour |