bos-settings: first-pass --screenshot CLI mode for automated capture

First bread-ecosystem app on the Tauri/webview stack rather than raw
GTK4 — proves the isolated-headless-Sway capture pipeline works against
a plain (non-layer-shell) tao/wry window with no gtk4-rs-specific signal
to hook. No connect_map here: since the window isn't owned by gtk4-rs
directly, this instead waits a fixed settle delay (2s — longer than the
native apps need, since a webview's first paint means a full page load
plus an async Tauri-command round-trip for real content, not just GTK
widget layout — confirmed by an initial 800ms attempt capturing the
sidebar correctly but the About panel's data still blank) on Tauri's own
async runtime, then captures the known-size canvas and exits.

Only one view ("default", the initial landing section) is wired up.
Capturing a specific sidebar section would mean routing the Svelte
frontend to a URL/hash on window creation — real, separate frontend
work, deferred past this first pass.

bread-screenshots is pulled from bread-ecosystem's dev branch, unlike
this repo's existing bread-theme/bread-utils deps which point at main —
it doesn't exist on main yet.

src/Cargo.toml

@@ -43,4 +43,8 @@ regex = "1"
 # checkout exists on the runner) since no tag has these functions yet.
 bread-theme = { git = "https://github.com/Breadway/bread-ecosystem", branch = "main" }
 bread-utils = { git = "https://github.com/Breadway/bread-ecosystem", branch = "main", features = ["toml"] }
+# Capture primitives for `--screenshot` mode — see src/screenshot.rs. On
+# "dev", not "main" like the two deps above: it doesn't exist on main yet.
+bread-screenshots = { git = "https://git.breadway.dev/Breadway/bread-ecosystem", branch = "dev" }
+anyhow = "1"