feat: add shareable lesson links with URL routing

- Add share button with SVG link icon in lesson title row
- Create share dialog with copy URL functionality
- Implement URL hash-based routing for lesson navigation
- Support browser back/forward navigation
- Add i18n translations for share dialog in all languages
- Position share button between title and completion badge
- Add RTL support for title row layout

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

src/helpers/router.js

@@ -0,0 +1,57 @@
+/**
+ * URL Router for Code Crispies
+ * Handles hash-based routing for shareable lesson links
+ * Format: #module-id/lesson-index (e.g., #flexbox/2)
+ */
+
+/**
+ * Parse current URL hash into module and lesson info
+ * @returns {{ moduleId: string, lessonIndex: number } | null}
+ */
+export function parseHash() {
+	const hash = window.location.hash.slice(1); // Remove '#'
+	if (!hash) return null;
+
+	const parts = hash.split("/");
+	if (parts.length !== 2) return null;
+
+	const moduleId = parts[0];
+	const lessonIndex = parseInt(parts[1], 10);
+
+	if (!moduleId || isNaN(lessonIndex) || lessonIndex < 0) return null;
+
+	return { moduleId, lessonIndex };
+}
+
+/**
+ * Update URL hash with history entry (for navigation)
+ * @param {string} moduleId
+ * @param {number} lessonIndex
+ */
+export function updateHash(moduleId, lessonIndex) {
+	const newHash = `#${moduleId}/${lessonIndex}`;
+	if (window.location.hash !== newHash) {
+		history.pushState(null, "", newHash);
+	}
+}
+
+/**
+ * Replace URL hash without history entry (for invalid URL fallbacks)
+ * @param {string} moduleId
+ * @param {number} lessonIndex
+ */
+export function replaceHash(moduleId, lessonIndex) {
+	const newHash = `#${moduleId}/${lessonIndex}`;
+	history.replaceState(null, "", newHash);
+}
+
+/**
+ * Build full shareable URL for current lesson
+ * @param {string} moduleId
+ * @param {number} lessonIndex
+ * @returns {string}
+ */
+export function getShareableUrl(moduleId, lessonIndex) {
+	const base = window.location.origin + window.location.pathname;
+	return `${base}#${moduleId}/${lessonIndex}`;
+}