Rename Text size to Interface; scale panel header with it

Action buttons, server picker, and its dropdown now follow the size
setting via new --action-h/--action-font/--action-icon variables.
Default tier matches the old fixed sizes; tab bar stays fixed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/styles.css

@@ -127,15 +127,19 @@
   --radius-lg: var(--radius);
 }
 
-/* Text-size setting for the path bar + file list (data-text set by SettingsService).
-   Also scales row height and the path-bar controls — compact matches the 24px
-   panel action buttons. */
+/* Interface-size setting (data-text set by SettingsService). Scales the whole
+   panel chrome: file list, path bar, action buttons, and the source picker
+   with its dropdown. The tab bar (including the options button) stays fixed.
+   Default-tier values match the old hardcoded classes exactly. */
 :root {
   --list-font: 13px;
   --list-meta-font: 12px;
   --path-font: 12px;
   --row-h: 28px;
   --path-ctl-h: 28px;
+  --action-h: 24px;
+  --action-font: 11px;
+  --action-icon: 0.9rem;
 }
 :root[data-text='compact'] {
   --list-font: 12px;
@@ -143,6 +147,9 @@
   --path-font: 11px;
   --row-h: 24px;
   --path-ctl-h: 24px;
+  --action-h: 22px;
+  --action-font: 10px;
+  --action-icon: 0.85rem;
 }
 :root[data-text='large'] {
   --list-font: 14px;
@@ -150,6 +157,9 @@
   --path-font: 13px;
   --row-h: 32px;
   --path-ctl-h: 32px;
+  --action-h: 28px;
+  --action-font: 12px;
+  --action-icon: 1.05rem;
 }
 
 /* Accent tone (data-accent set by SettingsService; absent = graphite/zinc).