refactor: use go:embed for templates

Templates are now embedded using //go:embed and parsed once at startup
with template.Must(template.ParseFS(...)). This avoids re-parsing
template files from disk on every request and removes the dependency
on template files being present at runtime.

closes #7

internal/handlers/profile.go

@@ -54,6 +54,6 @@ func (h *Handlers) HandleProfile() http.HandlerFunc {
 		}
 
 		// Render the profile page
-		h.renderTemplate(w, r, []string{"templates/base.html", "templates/profile.html"}, data)
+		h.renderTemplate(w, r, "profile.html", data)
 	}
 }