Fix boot-critical, session, and UX bugs found in round-3 UX audit

Snapshots panel was non-functional (wrong snapper flag); breadgreet picked
the wrong session .desktop and skipped bos-session's PATH fixup; Calamares
aborted offline installs over an unnecessary packages module; snapshot
rollback silently no-op'd on BOS's pinned-subvolume layout (now points at
grub-btrfs instead); breadcrumbs was configurable but had no daemon to run
it. Also: SUPER+I double-bind, breadpaper/packages panels blocking the GTK
main thread, dead polkit rule, and a sweep of smaller drift (default
sidebar view, stale wording, missing .desktop launchers, wallpaper daemon
not recording its own default).

bos-settings/src/ui/views/breadpaper.rs

@@ -0,0 +1,153 @@
+//! breadpaper — wallpaper manager. No config file to edit here; breadpaper
+//! takes no persistent settings, just an image path via its CLI (`breadpaper
+//! set <path>` / `breadpaper get`). This panel is a thin GUI front-end for
+//! that CLI so wallpaper (and the pywal-driven theme it generates) has a
+//! discoverable home in BOS Settings instead of only being reachable from a
+//! terminal.
+
+use std::path::PathBuf;
+use std::process::Command;
+
+use gtk4::prelude::*;
+use gtk4::{
+    Box as GBox, Button, FileChooserAction, FileChooserDialog, Image, Label, Orientation,
+    ResponseType,
+};
+
+use crate::ui::widgets as w;
+
+fn current_wallpaper() -> Option<PathBuf> {
+    let out = Command::new("breadpaper").arg("get").output().ok()?;
+    if !out.status.success() {
+        return None;
+    }
+    let s = String::from_utf8_lossy(&out.stdout).trim().to_string();
+    if s.is_empty() {
+        None
+    } else {
+        Some(PathBuf::from(s))
+    }
+}
+
+fn refresh_preview(preview: &Image, path_lbl: &Label) {
+    match current_wallpaper() {
+        Some(path) => {
+            path_lbl.set_text(&path.display().to_string());
+            preview.set_from_file(Some(&path));
+        }
+        None => {
+            path_lbl.set_text("No wallpaper set");
+            preview.set_icon_name(Some("image-missing"));
+        }
+    }
+}
+
+pub fn build() -> GBox {
+    let (outer, c) = w::view_scaffold("breadpaper");
+
+    c.append(&w::hint(
+        "Sets the desktop wallpaper, generates a matching pywal palette, and \
+         reloads the shared bread-theme stylesheet — the wallpaper drives \
+         the whole desktop's accent colors.",
+    ));
+
+    let preview = Image::new();
+    preview.set_pixel_size(320);
+    preview.set_margin_top(8);
+    preview.set_margin_bottom(8);
+    c.append(&preview);
+
+    let path_lbl = Label::new(None);
+    path_lbl.set_wrap(true);
+    path_lbl.add_css_class("dim-label");
+    c.append(&path_lbl);
+
+    refresh_preview(&preview, &path_lbl);
+
+    let btn_row = GBox::new(Orientation::Horizontal, 8);
+    btn_row.set_margin_top(8);
+
+    let choose_btn = Button::with_label("Choose image...");
+    let status = Label::new(None);
+    status.add_css_class("dim-label");
+
+    {
+        let preview = preview.clone();
+        let path_lbl = path_lbl.clone();
+        let status = status.clone();
+        choose_btn.connect_clicked(move |btn| {
+            let window = btn.root().and_then(|r| r.downcast::<gtk4::Window>().ok());
+            let dialog = FileChooserDialog::new(
+                Some("Choose a wallpaper"),
+                window.as_ref(),
+                FileChooserAction::Open,
+                &[("Cancel", ResponseType::Cancel), ("Set", ResponseType::Accept)],
+            );
+            // Restricted to what breadpaper's own validate() actually
+            // accepts (png/jpg/jpeg/webp/gif/bmp) — add_pixbuf_formats()
+            // also offers svg/tiff/etc. that breadpaper rejects outright.
+            let filter = gtk4::FileFilter::new();
+            for ext in ["png", "jpg", "jpeg", "webp", "gif", "bmp"] {
+                filter.add_suffix(ext);
+            }
+            filter.set_name(Some("Images"));
+            dialog.add_filter(&filter);
+
+            let preview = preview.clone();
+            let path_lbl = path_lbl.clone();
+            let status = status.clone();
+            dialog.connect_response(move |dialog, response| {
+                if response == ResponseType::Accept {
+                    if let Some(file) = dialog.file() {
+                        if let Some(path) = file.path() {
+                            // breadpaper set runs `awww img` + pywal palette
+                            // generation, which is routinely 1-3s (pywal
+                            // spawns Python + an ImageMagick backend) — not
+                            // the "sub-second" call this used to assume.
+                            // GTK widgets aren't Send, so run it in a thread
+                            // and hand the result back over a channel
+                            // (same pattern as snapshots.rs).
+                            status.set_text("Setting...");
+                            let (tx, rx) = async_channel::bounded::<bool>(1);
+                            std::thread::spawn(move || {
+                                let ok = Command::new("breadpaper")
+                                    .arg("set")
+                                    .arg(&path)
+                                    .status()
+                                    .map(|s| s.success())
+                                    .unwrap_or(false);
+                                let _ = tx.send_blocking(ok);
+                            });
+
+                            let preview = preview.clone();
+                            let path_lbl = path_lbl.clone();
+                            let status = status.clone();
+                            glib::spawn_future_local(async move {
+                                let ok = rx.recv().await.unwrap_or(false);
+                                if ok {
+                                    refresh_preview(&preview, &path_lbl);
+                                    status.set_text("Wallpaper set");
+                                } else {
+                                    status.set_text("breadpaper failed — see terminal/journal");
+                                }
+                                let lbl = status.clone();
+                                glib::timeout_add_seconds_local(3, move || {
+                                    lbl.set_text("");
+                                    glib::ControlFlow::Break
+                                });
+                            });
+                        }
+                    }
+                }
+                dialog.close();
+            });
+            dialog.show();
+        });
+    }
+
+    btn_row.append(&choose_btn);
+    btn_row.append(&status);
+    c.append(&btn_row);
+
+    outer
+}