release: v1.1.3 — dual-domain separation and URL options

Add admin/image domain separation with host isolation middleware,
optional hide-folder public URLs, GitHub release update check, and
Lucky/Nginx deployment docs. Switch license to GPL-3.0-only.

docs/domain-separation.en.md

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+# Dual-domain separation · Recommended deployment
+
+When admin and image domains are split, the admin UI, API, and public image links use different hostnames. PicHost enforces isolation in **application middleware**: the image host only serves image paths; other requests return 404.
+
+## Architecture
+
+**One Docker instance + two domains**, both **fully reverse-proxied** to port `6892` (isolation is handled by PicHost middleware; no path splitting in Nginx).
+
+| Domain | Purpose |
+| ------ | ------- |
+| `admin.example.com` | Admin UI, API, Twikoo upload |
+| `pic.example.com` | Public image links (non-image paths blocked) |
+
+Set during `/setup` or in **Settings**:
+
+- **Site URL**: `https://admin.example.com`
+- **Image URL**: `https://pic.example.com`
+
+## Nginx example
+
+```nginx
+# admin.example.com — admin + API + images
+server {
+  server_name admin.example.com;
+  location / {
+    proxy_pass http://127.0.0.1:6892;
+    proxy_set_header Host $host;
+    proxy_set_header X-Forwarded-Proto $scheme;
+    client_max_body_size 12m;
+  }
+}
+
+# pic.example.com — same full proxy; PicHost middleware blocks non-image paths
+server {
+  server_name pic.example.com;
+  location / {
+    proxy_pass http://127.0.0.1:6892;
+    proxy_set_header Host $host;
+    proxy_set_header X-Forwarded-Proto $scheme;
+  }
+}
+```
+
+> Caddy, NPM, and similar tools work the same: proxy both hostnames to `http://<host>:6892` and forward `Host` and `X-Forwarded-Proto`.
+
+## FN NAS · Lucky reverse proxy
+
+In [Lucky](https://github.com/gdy666/lucky), create one **reverse proxy** rule per domain. **Frontend** is the public hostname; **backend** is PicHost on your LAN (e.g. `http://192.168.8.3:6892`).
+
+**Site domain (admin)**
+
+| Field | Example |
+| ----- | ------- |
+| Service type | Reverse proxy |
+| Frontend | `admin.pichost.com` |
+| Backend | `http://192.168.8.3:6892` |
+
+![Lucky site domain](screenshots/lucky-site.png)
+
+**Image domain**
+
+| Field | Example |
+| ----- | ------- |
+| Service type | Reverse proxy |
+| Frontend | `image.pichost.com` |
+| Backend | `http://192.168.8.3:6892` |
+
+![Lucky image domain](screenshots/lucky-image.png)
+
+Both rules can point to the same backend; PicHost applies host-based isolation automatically.
+
+## Environment variables (optional)
+
+```env
+SITE_BASE_URL=https://admin.example.com
+IMAGE_BASE_URL=https://pic.example.com
+```
+
+## Notes
+
+- Hostnames must **differ** (same machine, different subdomains is fine)
+- No separate static root on the image domain; unlike EasyImages, PicHost isolates in-app
+- Single-domain setups can skip separation and use `IMAGE_BASE_URL` or the request host