shell theme: add glass-workbench as a second compiled-in theme

Phase 5 of the shell theme system (THEME_SYSTEM_PLAN.md §11): a second
builtin, demo 02's flush edge-to-edge bar with pill workspaces, a plain
date+time clock, and cpu/ram chips instead of the media widget.

- bread-theme/assets/shell/glass-workbench/: theme.toml + CSS template,
  faithful to bos-ui-demos/02-glass-workbench.html. Accent maps to the
  `green` palette token (flat, not a gradient) rather than a hex literal,
  so pywal theming still works.
- builtin.rs: generalized from a single hardcoded liquid-motion constant
  pair to a small BuiltinTheme registry (builtin::ALL / builtin::find),
  so mod.rs's discovery/list()/resolve_builtin no longer special-case one
  id. liquid-motion stays the pinned fallback in resolve_builtin().
- manifest.rs: KNOWN_MODULES gains "cpu"/"ram".
- types.rs: new Tokens::bar_border() ("full" default vs "bottom") so a
  flush bar can ask for a single hairline instead of an island's full
  border.
- Tests: builtin loads, appears in list() alongside liquid-motion, and its
  window spec is the flush/edge shape (36px, zero margin, radius 0).

cargo test -p bread-theme --lib: 63 passing (59 prior + 4 new).

bread-theme/src/shell/manifest.rs

@@ -29,6 +29,11 @@ const KNOWN_MODULES: &[&str] = &[
     "control",
     "launcher_entry",
     "launcher_results",
+    // `02-glass-workbench` (plan §11 phase 5): plain right-side stat chips,
+    // reusing the same `AppInput::StatsUpdate` data the control panel's
+    // sys-grid already receives — see breadbar's `bar::slots` module docs.
+    "cpu",
+    "ram",
 ];
 
 pub(super) fn validate_module_name(theme_id: &str, slot: &str, module: &str) -> anyhow::Result<()> {