restore semantic bold rendering in terminal panes (T-73)

Bold attributes from terminal escapes now render in a real bold
weight instead of being silently flattened.

- pubspec.yaml: register JetBrainsMono Bold + BoldItalic at
  weight 700 under family JetBrainsMono. Files already shipped on
  disk; only the registration was missing.
- assets/licenses.yaml: bump JetBrainsMono weights_bundled to
  [Regular, Italic, Bold, BoldItalic] per D-42 (the entry must
  match what is actually wired into the family).
- lib/src/terminal/src/ui/painter.dart: revert the `bold: false`
  override and drop the workaround comment. Bold now flows from
  CellFlags.bold to TextStyle.fontWeight.
- test/terminal/painter_bold_metrics_test.dart: load Regular and
  Bold via FontLoader and assert paragraph maxIntrinsicWidth is
  identical (cell-grid drift = 0). JetBrainsMono Bold's monospace
  by spec; this test is the canary for the day someone swaps the
  font.
- test/goldens/goldens/{ci,linux}/clide_button.png: regenerate.
  ClideButton's label renders slightly heavier on the bold variant
  (expected — 0.28% pixel diff before regen).

Earlier perception of over-bolding in the Claude pane was
synthetic-bold smearing (Flutter overpaints when no Bold.ttf is
registered for the family), not legitimate bold rendering. Visual
A/B confirms a real Bold face renders crisp emphasis without the
smear, so no per-pane renderer config is needed.

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

test/terminal/painter_bold_metrics_test.dart

@@ -0,0 +1,55 @@
+/// Verifies that the bundled JetBrainsMono Bold face has identical
+/// advance widths to Regular at our render size — required for the
+/// terminal cell grid to stay stable when bold attributes flip on.
+///
+/// If this fails, the workaround in painter.dart was deactivated
+/// against a font that drifts; pick one of the alternatives in T-73
+/// (variable JetBrainsMono / Berkeley Mono / IBM Plex Mono).
+library;
+
+import 'dart:io';
+import 'dart:ui' as ui;
+
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+const _family = 'JetBrainsMonoTest';
+const _fontSize = 14.0;
+const _sample = 'mmmmmmmmmm';
+
+void main() {
+  setUpAll(() async {
+    final regular = await File('assets/fonts/jetbrains_mono/JetBrainsMono-Regular.ttf').readAsBytes();
+    final bold = await File('assets/fonts/jetbrains_mono/JetBrainsMono-Bold.ttf').readAsBytes();
+
+    final loader = FontLoader(_family)
+      ..addFont(Future.value(ByteData.sublistView(regular)))
+      ..addFont(Future.value(ByteData.sublistView(bold)));
+    await loader.load();
+  });
+
+  test('JetBrainsMono Bold advance width matches Regular (cell drift = 0)', () {
+    final regularWidth = _measure(FontWeight.normal);
+    final boldWidth = _measure(FontWeight.bold);
+    expect(boldWidth, regularWidth,
+        reason: 'Bold advance width must equal Regular at $_fontSize px '
+            'or the terminal cell grid drifts when bold flips on.');
+  });
+}
+
+double _measure(FontWeight weight) {
+  final builder = ui.ParagraphBuilder(ui.ParagraphStyle(
+    fontFamily: _family,
+    fontSize: _fontSize,
+  ))
+    ..pushStyle(ui.TextStyle(
+      fontFamily: _family,
+      fontWeight: weight,
+      fontSize: _fontSize,
+    ))
+    ..addText(_sample);
+  final paragraph = builder.build()..layout(const ui.ParagraphConstraints(width: double.infinity));
+  final width = paragraph.maxIntrinsicWidth;
+  paragraph.dispose();
+  return width;
+}