feat(theme): themes as files (theme crate: toml subset + ints, contrast check, wire); whimsy dark + light; display reads themes/, serves THEME/THEME_NAME, init SET_THEME -> THEME_CHANGED to all windows, bar themed; k-ui follows; settings appearance; init keeps choice in sealed users/<id>/settings/, reapplies at sign-in + display restart

Cargo.toml

@@ -6,6 +6,7 @@ members = [
     "crates/apps/flaky",
     "crates/apps/tally",
     "crates/apps/settings",
+    "crates/theme",
     "crates/apps/hello",
     "crates/apps/shell",
     "crates/apps/cat",
@@ -81,6 +82,7 @@ types = { path = "crates/types" }
 domain = { path = "crates/domain" }
 elf = { path = "crates/elf" }
 manifest = { path = "crates/manifest" }
+theme = { path = "crates/theme" }
 keystore = { path = "crates/keystore" }
 filecrypt = { path = "crates/filecrypt" }
 # Audited RustCrypto implementations; never our own.