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>

ritz/llvm_codegen_signals.py

@@ -916,11 +916,6 @@ class SignalLLVMIRGenerator:
         else:
             self.lines.append(f"  %{elem_var} = call i32 @render_{component_name}()")
 
-        # Append to parent if we have one
-        if self.parent_element_stack:
-            parent_var = self.parent_element_stack[-1]
-            self.lines.append(f"  call void @js_append_child(i32 %{parent_var}, i32 %{elem_var})")
-
         return elem_var
 
     def _emit_match(self, stmt: dict[str, Any]) -> str | None:
@@ -1165,11 +1160,6 @@ class SignalLLVMIRGenerator:
         # Pop parent
         self.parent_element_stack.pop()
 
-        # If we're inside an if/match branch (have a grandparent), append to it
-        if self.parent_element_stack:
-            parent_var = self.parent_element_stack[-1]
-            self.lines.append(f"  call void @js_append_child(i32 %{parent_var}, i32 %{elem_var})")
-
         return elem_var
 
     def _emit_yield(self, stmt: dict[str, Any]) -> str | None: