Add landing page, redesign emails, and return updated task on completion

- Integrate landing page into Go app (served at root /)
- Add STATIC_DIR config for static file serving
- Redesign all email templates with modern dark theme styling
- Add app icon to email headers
- Return updated task with kanban_column in completion response
- Update task DTO to include kanban column for client-side state updates

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

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

static/js/main.js

@@ -0,0 +1,82 @@
+/**
+ * Casera Landing Page JavaScript
+ */
+
+document.addEventListener('DOMContentLoaded', function() {
+    // Mobile Navigation Toggle
+    const navToggle = document.getElementById('nav-toggle');
+    const navLinks = document.getElementById('nav-links');
+
+    if (navToggle && navLinks) {
+        navToggle.addEventListener('click', function() {
+            navLinks.classList.toggle('active');
+            navToggle.classList.toggle('active');
+        });
+
+        // Close menu when clicking a link
+        navLinks.querySelectorAll('.nav-link').forEach(link => {
+            link.addEventListener('click', () => {
+                navLinks.classList.remove('active');
+                navToggle.classList.remove('active');
+            });
+        });
+    }
+
+    // Smooth Scroll for Anchor Links
+    document.querySelectorAll('a[href^="#"]').forEach(anchor => {
+        anchor.addEventListener('click', function(e) {
+            const href = this.getAttribute('href');
+            if (href === '#') return;
+
+            e.preventDefault();
+            const target = document.querySelector(href);
+
+            if (target) {
+                const navHeight = document.querySelector('.nav').offsetHeight;
+                const targetPosition = target.getBoundingClientRect().top + window.pageYOffset - navHeight;
+
+                window.scrollTo({
+                    top: targetPosition,
+                    behavior: 'smooth'
+                });
+            }
+        });
+    });
+
+    // Scroll Animation Observer
+    const observerOptions = {
+        threshold: 0.1,
+        rootMargin: '0px 0px -50px 0px'
+    };
+
+    const observer = new IntersectionObserver((entries) => {
+        entries.forEach(entry => {
+            if (entry.isIntersecting) {
+                entry.target.classList.add('animate-in');
+                observer.unobserve(entry.target);
+            }
+        });
+    }, observerOptions);
+
+    // Observe elements for animation
+    document.querySelectorAll('.feature, .highlight-card, .testimonial-card, .platforms-content').forEach(el => {
+        el.style.opacity = '0';
+        observer.observe(el);
+    });
+
+    // Nav Background on Scroll
+    const nav = document.querySelector('.nav');
+    let lastScroll = 0;
+
+    window.addEventListener('scroll', () => {
+        const currentScroll = window.pageYOffset;
+
+        if (currentScroll > 50) {
+            nav.style.boxShadow = 'var(--shadow-md)';
+        } else {
+            nav.style.boxShadow = 'none';
+        }
+
+        lastScroll = currentScroll;
+    });
+});