breadman: add --screenshot CLI mode for automated capture

Same reasoning as breadpad, extending breadman's own hand-rolled arg
parser rather than adding clap. --screenshot <view> doubles as the view
selector — breadman already supports opening directly to a named stack
page via --view/initial_view, so this just feeds that same mechanism
instead of needing a separate one. Full known-size canvas capture, plain
top-level window (not layer-shell).

Also fixes the same NON_UNIQUE footgun as breadpad/breadbox/etc.

breadman/src/screenshot.rs

@@ -0,0 +1,58 @@
+//! `--screenshot` CLI mode: render the named view, capture it via
+//! `bread-screenshots`, then exit — driven by `bread-ecosystem`'s
+//! `bread-capture` orchestrator, or run standalone for one-off captures.
+//!
+//! No clap here, same reasoning as breadpad: extends breadman's own
+//! hand-rolled `mod args` instead of bolting on a second parser that would
+//! reject its real flags (`--view`, `done`, `upcoming --plain`).
+//!
+//! `--screenshot <view>` doubles as the view selector — it's passed through
+//! as `initial_view` (the same field `--view` already sets) rather than
+//! needing a separate mechanism, since breadman already supports opening
+//! directly to a named stack page.
+
+use gtk4::prelude::*;
+use std::path::PathBuf;
+use std::time::Duration;
+
+/// Extra settle time after `map` for the first frame to actually paint
+/// before grim runs — `map` fires once the surface exists, not once
+/// anything has been drawn into it.
+const SETTLE_DELAY: Duration = Duration::from_millis(300);
+
+#[derive(Clone)]
+pub struct ScreenshotRequest {
+    pub view: String,
+    pub output: PathBuf,
+    pub width: u32,
+    pub height: u32,
+}
+
+/// Wire up the given view's screenshot sequence against an already-built,
+/// not-yet-presented window. Every path here ends by exiting the process —
+/// it never returns control to the normal note-manager UI.
+///
+/// Unlike the other apps' `dispatch`, this doesn't validate `req.view`
+/// against a known-views list — an invalid name just falls through to
+/// breadman's own `unwrap_or("all")` default (see `build_app_window`),
+/// same as `--view` already behaves for a normal run.
+pub fn dispatch(window: &gtk4::ApplicationWindow, req: ScreenshotRequest) {
+    let output = req.output;
+    let (width, height) = (req.width as i32, req.height as i32);
+    window.connect_map(move |_| {
+        let output = output.clone();
+        gtk4::glib::timeout_add_local_once(SETTLE_DELAY, move || {
+            finish(bread_screenshots::capture_region(0, 0, width, height, &output));
+        });
+    });
+}
+
+fn finish(result: anyhow::Result<()>) {
+    match result {
+        Ok(()) => std::process::exit(0),
+        Err(e) => {
+            eprintln!("breadman: screenshot capture failed: {e}");
+            std::process::exit(1);
+        }
+    }
+}