Add NewSQLiteSessionManager helper that creates an SCS session manager
backed by SQLite, allowing sessions to persist across server restarts.
The function handles table creation automatically.
Add SSE-based navigation methods to Context:
- Redirect(url) / Redirectf() - navigate to new page
- ReplaceURL(url) / ReplaceURLf() - update URL without navigation
Update session example to demonstrate full login flow with redirects.
