Implement RitzMain() convention and Main.wasm standard

**Convention: RitzMain() entry point**
Every Ritz file now requires a `@component def RitzMain()` as the entry point.
This provides a consistent, predictable entry point for all applications.

**Universal Main.wasm output**
Build system now always outputs Main.wasm instead of ComponentName.wasm.
This means every example uses the exact same HTML boilerplate!

**Changes:**

**Codegen (llvm_codegen_signals.py):**
- Check for RitzMain component at generation time
- Error if RitzMain not found: "No RitzMain component found!"
- Always call `render_RitzMain()` from main() entry point
- Fix: Scope reactive text nodes to components (`@reactive_text_ComponentName_N_node`)
  - Prevents global name collisions when multiple components have reactive text

**Build (build.py):**
- Output Main.wasm in same directory as source file
- Output Main.ll (LLVM IR) for inspection
- Convention over configuration!

**Loader (ritz-runtime.js):**
- Auto-detect component name from WASM filename
- `new RitzLoader().load('Main.wasm')` - no second parameter needed!
- Component name used only for status messages

**Template (examples/template.html):**
- Minimal boilerplate - literally 25 lines
- Just copy and change nothing!
- Loads Main.wasm - works for every example

**Styles (examples/runtime/styles.css):**
- Shared styles for all examples
- Clean, modern defaults
- App container, buttons, inputs, typography

**Example (HighFive):**
```python
@component
def HighFive():
    # ... component logic

@component
def RitzMain():
    """Entry point - required!"""
    yield HighFive()
```

**Result:**
✅ Every example: copy template.html, change nothing
✅ Every example: builds to Main.wasm
✅ Consistent entry point: RitzMain()
✅ No more component name boilerplate

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

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

examples/runtime/styles.css

@@ -0,0 +1,100 @@
+/* Ritz Framework - Shared Example Styles */
+
+* {
+    box-sizing: border-box;
+}
+
+body {
+    margin: 0;
+    font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
+    background: #f5f5f5;
+    color: #333;
+    line-height: 1.6;
+}
+
+#app {
+    max-width: 800px;
+    margin: 50px auto;
+    padding: 40px;
+    background: white;
+    border-radius: 8px;
+    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
+}
+
+#status {
+    position: fixed;
+    top: 20px;
+    right: 20px;
+    padding: 12px 20px;
+    background: #fff;
+    border: 1px solid #ddd;
+    border-radius: 6px;
+    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
+    font-size: 14px;
+}
+
+#status.success {
+    background: #d4edda;
+    border-color: #c3e6cb;
+    color: #155724;
+}
+
+#status.error {
+    background: #f8d7da;
+    border-color: #f5c6cb;
+    color: #721c24;
+}
+
+h1, h2, h3 {
+    margin-top: 0;
+    color: #222;
+}
+
+p {
+    margin: 15px 0;
+}
+
+button {
+    padding: 12px 24px;
+    font-size: 16px;
+    font-weight: 500;
+    background: #0066cc;
+    color: white;
+    border: none;
+    border-radius: 6px;
+    cursor: pointer;
+    transition: all 0.2s;
+}
+
+button:hover {
+    background: #0052a3;
+    transform: translateY(-1px);
+    box-shadow: 0 2px 4px rgba(0,0,0,0.2);
+}
+
+button:active {
+    transform: translateY(0);
+    box-shadow: none;
+}
+
+input, select, textarea {
+    padding: 10px;
+    font-size: 16px;
+    border: 1px solid #ddd;
+    border-radius: 4px;
+    font-family: inherit;
+}
+
+input:focus, select:focus, textarea:focus {
+    outline: none;
+    border-color: #0066cc;
+    box-shadow: 0 0 0 3px rgba(0,102,204,0.1);
+}
+
+ul {
+    padding-left: 20px;
+}
+
+li {
+    margin: 8px 0;
+}