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/Cargo.toml

@@ -11,6 +11,8 @@ path = "src/main.rs"
 
 [dependencies]
 breadpad-shared = { path = "../breadpad-shared" }
+# Capture primitives for `--screenshot` mode — see src/screenshot.rs.
+bread-screenshots = { git = "https://git.breadway.dev/Breadway/bread-ecosystem", branch = "dev" }
 anyhow.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true