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/auth.go

@@ -21,7 +21,7 @@ func (h *Handlers) HandleLoginPage() http.HandlerFunc {
 			"Error": "",
 		}
 
-		h.renderTemplate(w, r, []string{"templates/base.html", "templates/login.html"}, data)
+		h.renderTemplate(w, r, "login.html", data)
 	}
 }
 
@@ -44,7 +44,7 @@ func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {
 				"Error": "Username and password are required",
 			}
 			w.WriteHeader(http.StatusBadRequest)
-			h.renderTemplate(w, r, []string{"templates/base.html", "templates/login.html"}, data)
+			h.renderTemplate(w, r, "login.html", data)
 			return
 		}
 
@@ -56,7 +56,7 @@ func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {
 				"Error": "Invalid username or password",
 			}
 			w.WriteHeader(http.StatusUnauthorized)
-			h.renderTemplate(w, r, []string{"templates/base.html", "templates/login.html"}, data)
+			h.renderTemplate(w, r, "login.html", data)
 			return
 		}
 
@@ -74,7 +74,7 @@ func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {
 				"Error": "Invalid username or password",
 			}
 			w.WriteHeader(http.StatusUnauthorized)
-			h.renderTemplate(w, r, []string{"templates/base.html", "templates/login.html"}, data)
+			h.renderTemplate(w, r, "login.html", data)
 			return
 		}