Fix duplicate append bug and componentize tabs

**Bug Fixes:**
- Fixed duplicate js_append_child calls causing DOM element re-insertion
- Elements were being appended twice: once by self-append logic, once by parent loop
- This was breaking CSS transitions on vertical tabs (elements moved in DOM)
- Removed self-append logic from _emit_with() and _emit_yield_component()

**Refactoring:**
- Created reusable HTab and VTab components for horizontal/vertical tabs
- Reduced repetitive tab code from 9 lines per tab to 1 line
- Improved code maintainability and reusability
- WASM bundle size reduced from 5987 bytes to 4690 bytes (22% reduction!)

**Result:**
- CSS transitions now work smoothly on vertical tabs ✓
- All 55 tests passing ✓
- Cleaner, more composable tab components ✓

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

examples/tabs/Tabs.py

@@ -11,6 +11,35 @@ Demonstrates:
 from ritz.syntax import *
 
 
+# ===== Reusable Tab Components =====
+
+@component
+def HTab(label, active, onclick):
+    """Horizontal tab (Li > Button structure).
+
+    Args:
+        label: String - tab label text
+        active: Boolean - whether this tab is active
+        onclick: Function - click handler
+    """
+    with Li(class_='tab active' if active else 'tab'):
+        with Button(onclick=onclick):
+            yield label
+
+
+@component
+def VTab(label, active, onclick):
+    """Vertical tab button.
+
+    Args:
+        label: String - tab label text
+        active: Boolean - whether this tab is active
+        onclick: Function - click handler
+    """
+    with Button(class_='vertical-tab active' if active else 'vertical-tab', onclick=onclick):
+        yield label
+
+
 @component
 def VerticalTabs():
     """Vertical tabs for settings categories."""
@@ -20,19 +49,11 @@ def VerticalTabs():
         setting_tab = value
 
     with Div(class_="vertical-tabs"):
-        # Vertical tab menu - clean ternary syntax!
+        # Vertical tab menu - using reusable VTab component!
         with Div(class_="vertical-tab-menu"):
-            with Button(class_='vertical-tab active' if setting_tab == 0 else 'vertical-tab',
-                        onclick=lambda: set_setting(0)):
-                yield "⚙️ General"
-
-            with Button(class_='vertical-tab active' if setting_tab == 1 else 'vertical-tab',
-                        onclick=lambda: set_setting(1)):
-                yield "🔒 Privacy"
-
-            with Button(class_='vertical-tab active' if setting_tab == 2 else 'vertical-tab',
-                        onclick=lambda: set_setting(2)):
-                yield "🚀 Advanced"
+            yield VTab(label="⚙️ General", active=setting_tab == 0, onclick=lambda: set_setting(0))
+            yield VTab(label="🔒 Privacy", active=setting_tab == 1, onclick=lambda: set_setting(1))
+            yield VTab(label="🚀 Advanced", active=setting_tab == 2, onclick=lambda: set_setting(2))
 
         # Vertical tab content
         with Div(class_="vertical-tab-content"):
@@ -85,19 +106,11 @@ def Tabs(orientation=0):  # 0 = horizontal, 1 = vertical
         with P(class_="subtitle"):
             yield "Beautiful composition with TabMenu and TabPane components"
 
-        # Tab menu - clean ternary syntax!
+        # Tab menu - using reusable HTab component!
         with Ul(class_="tab-menu"):
-            with Li(class_='tab active' if tab_index == 0 else 'tab'):
-                with Button(onclick=lambda: set_tab(0)):
-                    yield "🏠 Home"
-
-            with Li(class_='tab active' if tab_index == 1 else 'tab'):
-                with Button(onclick=lambda: set_tab(1)):
-                    yield "👤 Profile"
-
-            with Li(class_='tab active' if tab_index == 2 else 'tab'):
-                with Button(onclick=lambda: set_tab(2)):
-                    yield "⚙️ Settings"
+            yield HTab(label="🏠 Home", active=tab_index == 0, onclick=lambda: set_tab(0))
+            yield HTab(label="👤 Profile", active=tab_index == 1, onclick=lambda: set_tab(1))
+            yield HTab(label="⚙️ Settings", active=tab_index == 2, onclick=lambda: set_tab(2))
 
         # Tab panes - match/case for clean switching
         with Div(class_="tab-content"):