add ssr-counter example demonstrating SSR + hydration end-to-end

Counter.el defines Counter, CounterPair, and App components with {#if}
conditionals, event handlers, and child component composition.

render.js (generated by elc-ui --target=server) is the Node.js render
script the server calls. app.js (generated by elc-ui --target=web) is the
compiled browser module. hydrate.js attaches the runtime to the
server-rendered DOM without replacing it.

index.html shows the integration point with instructions for injecting
server output and the two CLI commands needed to regenerate both targets.

examples/ssr-counter/render.js

@@ -0,0 +1,58 @@
+/**
+ * el-ui SSR render script — generated by elc-ui --target=server
+ * Source: Counter.el
+ *
+ * Exports:
+ *   renderToString(componentName, props)         -> HTML string
+ *   renderToDocument(componentName, props, opts) -> full HTML document
+ *   componentNames                               -> string[]
+ */
+'use strict';
+
+const { renderToString: _rts, renderToDocument: _rtd, parseComponents } = require('../../runtime/src/ssr.js');
+
+// Component source embedded at compile time
+const _src = Buffer.from('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', 'base64').toString('utf8');
+
+// Parse component names at module load time
+const _components = parseComponents(_src);
+const componentNames = [..._components.keys()];
+
+/**
+ * Render a component to an HTML string.
+ * @param {string} componentName
+ * @param {Object} [props={}]
+ * @returns {string}
+ */
+function renderToString(componentName, props = {}) {
+    return _rts(_src, componentName, props);
+}
+
+/**
+ * Render a component inside a full HTML document.
+ * @param {string} componentName
+ * @param {Object} [props={}]
+ * @param {Object} [shellOpts={}]
+ * @returns {string}
+ */
+function renderToDocument(componentName, props = {}, shellOpts = {}) {
+    return _rtd(_src, componentName, props, shellOpts);
+}
+
+module.exports = { renderToString, renderToDocument, componentNames };
+
+// CLI mode: node render.js <ComponentName> [propsJson]
+if (require.main === module) {
+    const compName = process.argv[2];
+    const propsJson = process.argv[3] || '{}';
+    if (!compName) {
+        console.error('Usage: node render.js <ComponentName> [propsJson]');
+        process.exit(1);
+    }
+    let props = {};
+    try { props = JSON.parse(propsJson); } catch (e) {
+        console.error('render.js: invalid props JSON:', e.message);
+        process.exit(1);
+    }
+    process.stdout.write(renderToString(compName, props));
+}