Drive bar/window geometry and CSS tokens from the shell theme manifest

breadbar no longer hardcodes BAR_HEIGHT/BAR_MARGIN_TOP/BAR_MARGIN_SIDES/
CHIP_HEIGHT/ICON_PX or the root window's layer-shell setup: it loads
bread_theme:🐚:ShellTheme once (theme::shell_theme(), cached in a
thread-local) and reads bar.window (anchors, margin, exclusive zone,
keyboard mode - now set explicitly instead of relying on the library
default) plus tokens.{icon_px,chip_height} from it everywhere those used
to be literals.

The four satellite surfaces (breadbar-osd, breadbar-notif, breadbar-panel,
breadbar-dismiss) now get their anchor/margin/width/layer from the
manifest's [surfaces.*] table via a small new surface::apply() helper,
narrowly scoped to the three anchor shapes those surfaces actually use.
The pre-existing 8px gap between the panel's top margin and the dismiss
scrim's is preserved exactly (and now commented) rather than "fixed".

theme.rs's load_css() keeps its ~250 lines of hand-written breadbar CSS
(notifications, wifi popover, control panel, media widget) but now reads
its five radius/pad locals and the two easing curves (spring vs
spring_settle - hover/settle transitions were previously miscategorized
as the overshoot curve in the constant audit; the actual code already
used the settle curve there, confirmed against src) from theme tokens
instead of hardcoding them.

Also wires bread_theme:🐚:watch() so editing the active theme's
theme.toml/extra.css hot-reloads CSS tokens without a restart, same as
a pywal palette change already does. Window-spec values still need a
restart per the plan (read once at window-construction time).

Verified pixel-identical: captured all 10 breadbar --screenshot views
(bar, control-panel, connectivity-wifi/bluetooth, media-popover,
notification/-critical, osd-volume/-brightness, wifi-add-dialog) via
bread-capture's isolated headless-Sway harness against both the
pre-change and post-change binaries; every view diffs byte-identical
at the decoded-pixel level.

Cargo.lock

@@ -186,12 +186,14 @@ dependencies = [
 [[package]]
 name = "bread-theme"
 version = "0.7.4"
-source = "git+https://git.breadway.dev/Breadway/bread-ecosystem?tag=v0.7.4#fcba3760387e2523edb71350f8efea3bc851b21e"
 dependencies = [
+ "anyhow",
  "dirs 5.0.1",
  "gtk4",
  "serde",
  "serde_json",
+ "toml 0.8.23",
+ "tracing",
 ]
 
 [[package]]