feat: add complete sidebar content to match original React CV

Comprehensive update to achieve feature parity with old React implementation.

## Data Layer (Backend)

**Updated Go Models** (internal/models/cv.go):
- Added Course struct (title, institution, location, date, duration, description)
- Added Reference struct (title, URL, type)
- Added Language.Detail field for proficiency descriptions
- Added CV.Courses and CV.References arrays

**Complete Data Population** (data/cv-es.json):
- Added 6 NEW skill categories (42 items):
  * Lenguajes de Programación (11 items: Java, Groovy, PHP, XML, XSLT, ActionScript, Shell, C, C++)
  * Frameworks PHP (4 items: Yii, Zend, WordPress API, Joomla API)
  * Frameworks Java (8 items: Play!, Struts, Spring, Hibernate, Ibatis, Magnolia CMS, XWiki, TESEO)
  * Servidores de Aplicaciones (9 items: Apache, WAMP, MAMP, Tomcat, JBoss, Resin, Jetty, Websphere, Weblogic)
  * CMS y Entornos (6 items: Joomla, WordPress, RapidWeaver, Servoy, WebRatio, Magnolia)
  * Herramientas de Diseño (4 items: Corel, Photoshop, Illustrator, GIMP)

- Updated existing categories with missing items:
  * Ecosistema JavaScript: +Redux, Flux, Gulp, Grunt
  * Desarrollo Web: +JSP, PHP, Handlebars, Moustache, Velocity, Freemarker, jQuery, mooTools, DOM, Ajax, SEO, WebServices
  * Bases de Datos: +Hypersonic, Dominio de SQL
  * Soft Skills: +5 team management items

- Added Catalan language (Comprensión, Level 2)
- Added detail field to all languages (oral/written breakdown)

- Added 4 courses:
  * Servoy World 2011 (Amsterdam, 3 días)
  * Formador de Formadores (FOREM, 150 horas)
  * Windows 2003 Server (Cámara de Comercio, 80 horas)
  * I Jornada Extremeña (Universidad, 3 días)

- Added 8 references:
  * Recommendation letters, portfolios, profiles, CVs

- Fixed driver's license: Tipo C → Tipo B

## Presentation Layer (Frontend)

**Template Updates** (templates/cv-content.html, templates/index.html):
- Skills section: Now renders ALL 13 categories dynamically
- Languages section: Added detail field display
- NEW Courses section: Full course details with institutions
- NEW References section: Clickable links with security attributes
- NEW Other section: Driver's license display
- Responsive grid layout maintained
- Conditional rendering (sections only show if data exists)

**Styling** (static/css/main.css):
- Added .course-item, .course-desc styles
- Added .reference-item, .ref-type styles
- Added .language-detail styles
- Maintained consistent sidebar section styling

## Impact

**Before**: 7 skill categories, 3 languages, 0 courses, 0 references
**After**: 13 skill categories (+6), 4 languages (+1), 4 courses (+4), 8 references (+8)
**Total**: 90+ new data points added

Sidebar now matches original React CV feature-for-feature.

static/css/main.css

@@ -427,6 +427,73 @@ a:hover {
 .language-item {
     font-size: 0.9rem;
     color: var(--text-dark);
+    margin-bottom: 0.5rem;
+}
+
+.language-item small {
+    display: block;
+    font-size: 0.8em;
+    margin-top: 0.2rem;
+    font-style: italic;
+}
+
+/* Courses */
+.course-item {
+    margin-bottom: 1rem;
+    padding-bottom: 0.8rem;
+    border-bottom: 1px solid rgba(0, 0, 0, 0.1);
+}
+
+.course-item:last-child {
+    border-bottom: none;
+    padding-bottom: 0;
+    margin-bottom: 0;
+}
+
+.course-item strong {
+    font-size: 0.95em;
+    color: var(--text-dark);
+    line-height: 1.3;
+}
+
+.course-item small {
+    display: block;
+    font-size: 0.85em;
+    color: var(--text-gray);
+    margin-top: 0.2rem;
+}
+
+.course-desc {
+    font-size: 0.85em;
+    color: var(--text-gray);
+    margin-top: 0.4rem;
+    line-height: 1.4;
+    text-align: justify;
+}
+
+/* References */
+.reference-item {
+    margin-bottom: 0.6rem;
+    line-height: 1.4;
+}
+
+.reference-item a {
+    font-size: 0.9em;
+    color: var(--accent-blue);
+    text-decoration: none;
+    word-break: break-word;
+}
+
+.reference-item a:hover {
+    text-decoration: underline;
+}
+
+.ref-type {
+    display: block;
+    font-size: 0.8em;
+    color: var(--text-gray);
+    font-style: italic;
+    margin-top: 0.2rem;
 }
 
 /* Footer */