fix: render simple table rows instead of project sections

Fix table alignment issue on landing page by rendering simple table
rows instead of collapsible project sections inside the tbody.

Changes:
- Simplify renderSessionsGroupedByProject() to render table rows directly
- Add table-layout: fixed to .projects-table for proper column widths
- Sort sessions by last activity (newest first)

The previous implementation was rendering div elements (project sections)
inside the table tbody, which broke the table layout. Table elements
only accept tr elements as direct children.

Resolves "things don't align" issue on projects table.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

public/claude-ide/sessions-landing.css

@@ -121,6 +121,7 @@ body.sessions-page {
 .projects-table {
     width: 100%;
     border-collapse: collapse;
+    table-layout: fixed;
 }
 
 .projects-table thead {