add type scale constants; remove scattered font size overrides

Sidebar and panel text was too small — dozens of bare fontSize:
10/11/12 values fighting the ambient DefaultTextStyle. Root font
bumped from 13 to 14. Three semantic constants replace the magic
numbers: clideFontBody (14), clideFontCaption (12), clideFontMono
(13). Widgets that render body text now inherit instead of
overriding.

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

app/lib/widgets/src/clide_pane_chrome.dart

@@ -5,6 +5,7 @@ import 'clide_divider.dart';
 import 'clide_icon.dart';
 import 'clide_text.dart';
 import 'icons/x.dart';
+import 'typography.dart';
 
 /// Shared chrome for any pane that sits in a tab or split: a title
 /// strip at the top, an optional close button, and the pane body
@@ -146,7 +147,7 @@ class _Header extends StatelessWidget {
                   children: [
                     ClideText(
                       title,
-                      fontSize: 12,
+                      fontSize: clideFontCaption,
                       color: tokens.panelHeaderForeground,
                       maxLines: 1,
                       overflow: TextOverflow.ellipsis,
@@ -154,7 +155,7 @@ class _Header extends StatelessWidget {
                     if (subtitle != null)
                       ClideText(
                         subtitle!,
-                        fontSize: 11,
+                        fontSize: clideFontCaption,
                         muted: true,
                         maxLines: 1,
                         overflow: TextOverflow.ellipsis,

app/lib/widgets/src/clide_pty_view.dart

@@ -20,7 +20,7 @@ class ClidePtyView extends StatelessWidget {
     this.label,
     this.focusNode,
     this.autofocus = false,
-    this.fontSize = 13,
+    this.fontSize = clideFontMono,
   });
 
   final Terminal terminal;

app/lib/widgets/src/clide_text.dart

@@ -15,7 +15,7 @@ class ClideText extends StatelessWidget {
     this.data, {
     super.key,
     this.color,
-    this.fontSize = 13,
+    this.fontSize = 14,
     this.fontFamily,
     this.fontWeight,
     this.muted = false,

app/lib/widgets/src/typography.dart

@@ -46,6 +46,17 @@ const List<String> clideUiFamilyFallback = [
 /// The bundled monospace family. Always resolved first.
 const String clideMonoFamily = 'JetBrainsMono';
 
+// ---------------------------------------------------------------------------
+// Type scale — semantic sizes. Widgets inherit from the ambient
+// DefaultTextStyle (set at the app root). Only override when the
+// semantic role genuinely differs from body text. Prefer these
+// constants over bare numbers so the scale stays coherent.
+// ---------------------------------------------------------------------------
+
+const double clideFontBody = 14;
+const double clideFontCaption = 12;
+const double clideFontMono = 13;
+
 /// System fallback chain. Ordered by platform prevalence + quality of
 /// programming-ligature / box-drawing coverage.
 const List<String> clideMonoFamilyFallback = [