fix(installer): add src/ deploy + drop MakeDirectory=yes; bump 1.3.1

- install.sh now deploys the src/ directory alongside routes/.
  Without this, fresh installs of v1.3.0+ produce containers whose
  Dockerfile references src/ but the directory is missing on the host
  filesystem, so docker build fails with "/src: not found".

- The fallback heredoc that writes /etc/systemd/system/dashcaddy-
  updater.path drops MakeDirectory=yes for the same reason it was
  removed from the on-disk unit (e994ad1): systemd creates the watched
  trigger.json path as an empty directory on unit start, blocking
  every subsequent update with EISDIR.

Bumped to 1.3.1 so the existing v1.3.0 instance auto-updates and
picks up these and the host-script fix from 0cf6323.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dashcaddy-api/package.json

@@ -1,6 +1,6 @@
 {
   "name": "dashcaddy-api",
-  "version": "1.3.0",
+  "version": "1.3.1",
   "description": "DashCaddy API server - Dashboard backend for Docker, Caddy & DNS management",
   "main": "server.js",
   "scripts": {