fix: inject <base href> from base_path config; fix relative asset/nav links; add README

http/handlers.c

@@ -117,7 +117,7 @@ void handle_series_show(int fd, const char *qs) {
     buf_free(&inl);
 
     free(sid); free(title_raw); free(cover_raw); free(json);
-    send_page(fd, "Series", &b, "/series_show.js");
+    send_page(fd, "Series", &b, "series_show.js");
     buf_free(&b);
 }
 
@@ -226,7 +226,7 @@ void handle_downloads(int fd) {
                 "<button class='btn btn-r' onclick=cleanPartials()>clean partial files</button>"
                 "</div>"
                 "<div id=dl-table><p style='color:var(--dim)'>loading...</p></div>");
-    send_page(fd, "Downloads", &b, "/downloads.js");
+    send_page(fd, "Downloads", &b, "downloads.js");
     buf_free(&b);
 }