feat: add Markdig markdown rendering for blog posts

- Add Markdig NuGet package (0.38.0)
- Convert blog content from markdown to HTML in Post.cshtml.cs
- Display rendered HTML content instead of raw text
- Add comprehensive markdown styling (h1-h6, lists, tables, code, etc.)
- Use TaxBaik color scheme for markdown elements

Blog posts now render properly:
✅ Headings (#, ##, ###)
✅ Bold/italic text (**text**, *text*)
✅ Lists (-, *, ordered)
✅ Tables
✅ Code blocks
✅ Blockquotes
✅ Links

Styling follows TaxBaik brand:
- Primary color for headings
- Warm typography (Noto Sans KR)
- Consistent spacing and borders
- Mobile-responsive design

TaxBaik.Web/wwwroot/css/site.css

@@ -836,3 +836,141 @@ img {
     box-shadow: 0 0 0 6px rgba(46, 92, 78, 0.3);
     transform: scale(1.1);
 }
+
+/* ===== 마크다운 스타일 ===== */
+.markdown-body {
+    font-size: 1rem;
+    line-height: 1.8;
+    color: var(--color-text);
+}
+
+.markdown-body h1,
+.markdown-body h2,
+.markdown-body h3,
+.markdown-body h4,
+.markdown-body h5,
+.markdown-body h6 {
+    font-weight: 700;
+    margin-top: 1.5rem;
+    margin-bottom: 1rem;
+    color: var(--color-text);
+}
+
+.markdown-body h1 {
+    font-size: 1.8rem;
+    border-bottom: 2px solid var(--color-primary);
+    padding-bottom: 0.5rem;
+}
+
+.markdown-body h2 {
+    font-size: 1.5rem;
+    border-bottom: 1px solid var(--color-border);
+    padding-bottom: 0.3rem;
+}
+
+.markdown-body h3 {
+    font-size: 1.25rem;
+}
+
+.markdown-body h4 {
+    font-size: 1.1rem;
+}
+
+.markdown-body p {
+    margin-bottom: 1rem;
+}
+
+.markdown-body strong {
+    font-weight: 700;
+    color: var(--color-primary-dark);
+}
+
+.markdown-body em {
+    font-style: italic;
+    color: var(--color-text-light);
+}
+
+.markdown-body code {
+    background: var(--color-bg-alt);
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius-sm);
+    padding: 0.15rem 0.4rem;
+    font-family: 'Courier New', monospace;
+    font-size: 0.9rem;
+    color: #d63384;
+}
+
+.markdown-body pre {
+    background: var(--color-text);
+    color: #f8f8f8;
+    padding: 1rem;
+    border-radius: var(--radius-lg);
+    overflow-x: auto;
+    margin-bottom: 1rem;
+    line-height: 1.4;
+}
+
+.markdown-body pre code {
+    background: none;
+    border: none;
+    padding: 0;
+    color: inherit;
+    font-size: 0.9rem;
+}
+
+.markdown-body ul,
+.markdown-body ol {
+    margin-bottom: 1rem;
+    margin-left: 2rem;
+}
+
+.markdown-body li {
+    margin-bottom: 0.5rem;
+}
+
+.markdown-body blockquote {
+    border-left: 4px solid var(--color-primary);
+    padding-left: 1rem;
+    margin: 1rem 0;
+    color: var(--color-text-light);
+    font-style: italic;
+}
+
+.markdown-body table {
+    border-collapse: collapse;
+    width: 100%;
+    margin-bottom: 1rem;
+}
+
+.markdown-body table th,
+.markdown-body table td {
+    border: 1px solid var(--color-border);
+    padding: 0.75rem;
+    text-align: left;
+}
+
+.markdown-body table th {
+    background: var(--color-bg-alt);
+    font-weight: 700;
+}
+
+.markdown-body table tr:nth-child(even) {
+    background: var(--color-bg);
+}
+
+.markdown-body a {
+    color: var(--color-primary-dark);
+    text-decoration: none;
+    border-bottom: 1px solid var(--color-primary);
+    transition: color var(--transition-fast);
+}
+
+.markdown-body a:hover {
+    color: var(--color-primary);
+}
+
+.markdown-body hr {
+    border: none;
+    border-top: 1px solid var(--color-border);
+    margin: 2rem 0;
+}