add sidebar icon rail replacing top tab bar

Four new icon painters (git branch, search, terminal, warning).
ClideIconRail widget with parent-owned hover state so only one
icon highlights at a time. Sidebar slot renders content above +
icon rail below; workspace and context slots keep the tab bar.

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

app/lib/widgets/src/icons/git_branch.dart

@@ -0,0 +1,27 @@
+import 'dart:ui';
+import 'package:clide_app/widgets/src/clide_icon.dart';
+
+class GitBranchIcon extends ClideIconPainter {
+  const GitBranchIcon();
+
+  @override
+  void paint(Canvas canvas, Color color) {
+    final paint = Paint()
+      ..color = color
+      ..style = PaintingStyle.stroke
+      ..strokeWidth = 0.08
+      ..strokeCap = StrokeCap.round;
+    // Trunk line
+    canvas.drawLine(const Offset(0.35, 0.2), const Offset(0.35, 0.8), paint);
+    // Branch line
+    canvas.drawLine(const Offset(0.65, 0.3), const Offset(0.65, 0.5), paint);
+    canvas.drawLine(const Offset(0.65, 0.5), const Offset(0.35, 0.6), paint);
+    // Dots at nodes
+    final dot = Paint()
+      ..color = color
+      ..style = PaintingStyle.fill;
+    canvas.drawCircle(const Offset(0.35, 0.2), 0.06, dot);
+    canvas.drawCircle(const Offset(0.35, 0.8), 0.06, dot);
+    canvas.drawCircle(const Offset(0.65, 0.3), 0.06, dot);
+  }
+}

app/lib/widgets/src/icons/search.dart

@@ -0,0 +1,17 @@
+import 'dart:ui';
+import 'package:clide_app/widgets/src/clide_icon.dart';
+
+class SearchIcon extends ClideIconPainter {
+  const SearchIcon();
+
+  @override
+  void paint(Canvas canvas, Color color) {
+    final paint = Paint()
+      ..color = color
+      ..style = PaintingStyle.stroke
+      ..strokeWidth = 0.08
+      ..strokeCap = StrokeCap.round;
+    canvas.drawCircle(const Offset(0.42, 0.42), 0.22, paint);
+    canvas.drawLine(const Offset(0.58, 0.58), const Offset(0.78, 0.78), paint);
+  }
+}

app/lib/widgets/src/icons/terminal_icon.dart

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+import 'dart:ui';
+import 'package:clide_app/widgets/src/clide_icon.dart';
+
+class TerminalIcon extends ClideIconPainter {
+  const TerminalIcon();
+
+  @override
+  void paint(Canvas canvas, Color color) {
+    final paint = Paint()
+      ..color = color
+      ..style = PaintingStyle.stroke
+      ..strokeWidth = 0.08
+      ..strokeCap = StrokeCap.round;
+    // Prompt chevron >_
+    canvas.drawLine(const Offset(0.2, 0.3), const Offset(0.45, 0.5), paint);
+    canvas.drawLine(const Offset(0.45, 0.5), const Offset(0.2, 0.7), paint);
+    // Cursor line
+    canvas.drawLine(const Offset(0.5, 0.7), const Offset(0.8, 0.7), paint);
+  }
+}

app/lib/widgets/src/icons/warning.dart

@@ -0,0 +1,28 @@
+import 'dart:ui';
+import 'package:clide_app/widgets/src/clide_icon.dart';
+
+class WarningIcon extends ClideIconPainter {
+  const WarningIcon();
+
+  @override
+  void paint(Canvas canvas, Color color) {
+    final paint = Paint()
+      ..color = color
+      ..style = PaintingStyle.stroke
+      ..strokeWidth = 0.08
+      ..strokeCap = StrokeCap.round
+      ..strokeJoin = StrokeJoin.round;
+    final path = Path()
+      ..moveTo(0.5, 0.15)
+      ..lineTo(0.85, 0.8)
+      ..lineTo(0.15, 0.8)
+      ..close();
+    canvas.drawPath(path, paint);
+    // Exclamation
+    canvas.drawLine(const Offset(0.5, 0.4), const Offset(0.5, 0.58), paint);
+    final dot = Paint()
+      ..color = color
+      ..style = PaintingStyle.fill;
+    canvas.drawCircle(const Offset(0.5, 0.68), 0.035, dot);
+  }
+}