fix(ui): Cyrillic/Greek weights, html lang, weight normalisation (#1780)

Load Roboto 600/700 and DM Sans 700 so Cyrillic and Greek headings render
real semibold and bold faces instead of a synthetic bold, keep
<html lang> in step with the UI language, and move every font weight onto
the 400/500/600/700 scale (JetBrains Mono at 500 or lighter; the dashboard
LIVE badge now uses the interface font at 700).

Add the `styles:font-weights:validate` ratchet guard and its CI step. It
reads stylesheets much as Sass and the browser do (cascade, layers,
mixins, content blocks, `@extend`, `@at-root`, `:is()`/`:where()`,
keyframes) and lists what it deliberately does not trace in its header.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/workspace/shell/feature/src/lib/global-favorites/global-favorites-list.component.scss

@@ -65,7 +65,7 @@
 
     .empty-title {
         font-size: 1.05rem;
-        font-weight: 520;
+        font-weight: 500;
         letter-spacing: -0.01em;
         margin: 0 0 8px;
     }

libs/workspace/shell/feature/src/lib/workspace-command-palette/workspace-command-palette.component.scss

@@ -44,7 +44,7 @@
     color: var(--mat-sys-on-surface);
     font: inherit;
     font-size: 0.94rem;
-    font-weight: 450;
+    font-weight: 500;
     width: 100%;
     min-width: 0;
 
@@ -188,7 +188,7 @@
 
 .palette-command__label {
     font-size: 0.84rem;
-    font-weight: 530;
+    font-weight: 500;
     letter-spacing: -0.006em;
     white-space: nowrap;
     overflow: hidden;

libs/workspace/shell/feature/src/lib/workspace-context-panel/components/workspace-context-category-view.component.scss

@@ -104,7 +104,7 @@ mat-card-content {
         --error-empty-illustration-size: clamp(132px, 15vw, 180px);
         --error-empty-max-width: min(270px, 100%);
         --error-empty-title-size: clamp(1.15rem, 1.35vw, 1.4rem);
-        --error-empty-title-weight: 610;
+        --error-empty-title-weight: 600;
         --error-empty-title-spacing: -0.006em;
         --error-empty-copy-gap: 4px;
         --error-empty-description-opacity: 0.82;

libs/workspace/shell/feature/src/lib/workspace-context-panel/components/workspace-context-error-view.component.scss

@@ -12,7 +12,7 @@
     --error-view-copy-width: var(--error-empty-max-width, 420px);
     --error-view-copy-gap: var(--error-empty-copy-gap, 8px);
     --error-view-title-size: var(--error-empty-title-size, 1.55rem);
-    --error-view-title-weight: var(--error-empty-title-weight, 640);
+    --error-view-title-weight: var(--error-empty-title-weight, 600);
     --error-view-title-spacing: var(--error-empty-title-spacing, -0.012em);
     --error-view-description-size: var(--error-empty-description-size, 0.98rem);
     --error-view-description-line-height: var(

libs/workspace/shell/feature/src/lib/workspace-keyboard-shortcuts/workspace-keyboard-shortcuts-dialog.component.scss

@@ -117,7 +117,7 @@
     border: 1px solid var(--shortcut-border);
     border-radius: 8px;
     font-size: 0.76rem;
-    font-weight: 650;
+    font-weight: 600;
     line-height: 1;
     white-space: nowrap;
 
@@ -186,7 +186,7 @@
     margin: 0;
     color: var(--shortcut-text);
     font-size: 0.74rem;
-    font-weight: 750;
+    font-weight: 700;
     line-height: 1.2;
     text-transform: uppercase;
 }
@@ -273,7 +273,7 @@
         0 1px 0 color-mix(in srgb, white 28%, transparent);
     font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
     font-size: 0.72rem;
-    font-weight: 750;
+    font-weight: 700;
     line-height: 1;
     white-space: nowrap;
 }

libs/workspace/shell/feature/src/lib/workspace-shell/components/workspace-shell-import-overlay/workspace-shell-import-overlay.component.scss

@@ -52,7 +52,7 @@
     h3 {
         margin: 0;
         font-size: 1.55rem;
-        font-weight: 650;
+        font-weight: 600;
         letter-spacing: -0.03em;
         color: var(--app-heading-color);
     }