feat: add landing pages and section navigation

- Add home landing page with section cards (CSS, HTML, Tailwind)
- Add section landing pages with module grid and progress tracking
- Implement extended URL routing for pages, sections, and lessons
- Create sections.js configuration for module categorization
- Exclude welcome/goodbye modules from progress stats
- Add main navigation links in header (desktop only)
- Update logo click to navigate to home landing

Routes:
- # → Home landing
- #css, #html, #tailwind → Section landing pages
- #module/index → Lesson (unchanged)

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

src/config/sections.js

@@ -0,0 +1,75 @@
+/**
+ * Section definitions for Code Crispies
+ * Sections group related modules (CSS, HTML, Tailwind)
+ */
+
+export const sections = {
+	css: {
+		id: "css",
+		title: "CSS",
+		description: "Styling, layout, and animations",
+		color: "#264de4",
+		order: 1
+	},
+	html: {
+		id: "html",
+		title: "HTML",
+		description: "Semantic markup and native elements",
+		color: "#e34c26",
+		order: 2
+	},
+	tailwind: {
+		id: "tailwind",
+		title: "Tailwind CSS",
+		description: "Utility-first CSS framework",
+		color: "#06b6d4",
+		order: 3
+	}
+};
+
+/**
+ * Get section by ID
+ * @param {string} sectionId
+ * @returns {object|null}
+ */
+export function getSection(sectionId) {
+	return sections[sectionId] || null;
+}
+
+/**
+ * Get all sections sorted by order
+ * @returns {object[]}
+ */
+export function getSectionList() {
+	return Object.values(sections).sort((a, b) => a.order - b.order);
+}
+
+/**
+ * Infer section from module mode
+ * @param {object} module
+ * @returns {string}
+ */
+export function getModuleSection(module) {
+	// Explicit section takes precedence
+	if (module.section) return module.section;
+
+	// Infer from mode
+	const mode = module.mode || "css";
+	if (mode === "html") return "html";
+	if (mode === "tailwind") return "tailwind";
+	return "css";
+}
+
+/**
+ * Filter modules by section
+ * @param {object[]} modules
+ * @param {string} sectionId
+ * @returns {object[]}
+ */
+export function getModulesBySection(modules, sectionId) {
+	return modules.filter((m) => {
+		// Skip excluded modules (welcome, goodbye)
+		if (m.excludeFromProgress) return false;
+		return getModuleSection(m) === sectionId;
+	});
+}