Add rendering routes and share UI to web server

The web UI was linking to /v1/ REST API paths that aren't served
through nginx. Added SVG/JPG/PDF rendering and share link endpoints
directly to the web server so everything works through port 443.

- Add render.go with SVG, JPG, PDF handlers for auth and share paths
- Register render routes and share management routes in web server
- Update template links from /v1/... to /notebooks/... paths
- Add share link creation, display, and revocation to notebook view

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/webserver/server.go

@@ -98,6 +98,9 @@ func Start(cfg Config) (*http.Server, error) {
 	// Share routes (no auth)
 	r.Get("/s/{token}", ws.handleShareNotebook)
 	r.Get("/s/{token}/pages/{num}", ws.handleSharePage)
+	r.Get("/s/{token}/pages/{num}/svg", ws.handleSharePageSVG)
+	r.Get("/s/{token}/pages/{num}/jpg", ws.handleSharePageJPG)
+	r.Get("/s/{token}/pdf", ws.handleSharePDF)
 
 	// Authenticated routes
 	r.Group(func(r chi.Router) {
@@ -106,6 +109,11 @@ func Start(cfg Config) (*http.Server, error) {
 		r.Get("/notebooks", ws.handleNotebooks)
 		r.Get("/notebooks/{id}", ws.handleNotebook)
 		r.Get("/notebooks/{id}/pages/{num}", ws.handlePage)
+		r.Get("/notebooks/{id}/pages/{num}/svg", ws.handlePageSVG)
+		r.Get("/notebooks/{id}/pages/{num}/jpg", ws.handlePageJPG)
+		r.Get("/notebooks/{id}/pdf", ws.handleNotebookPDF)
+		r.Post("/notebooks/{id}/share", ws.handleCreateShare)
+		r.Post("/notebooks/{id}/share/revoke", ws.handleRevokeShare)
 		r.Get("/logout", ws.handleLogout)
 
 		// WebAuthn authenticated routes (registration + key management)