fix samba write permissions and document UID requirement

The dperson/samba image uses UID/GID 1001 internally regardless of the
USERID env var. The host share directory must be owned by 1001:1001 for
writes to succeed. Add force user/group to smb.conf as an extra safety
net, and document the chown step in the README.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -26,6 +26,12 @@
    mkdir -p /home/padriano/share
    ```
 
+   The Samba container runs as UID/GID 1001 internally, so the share directory must be owned by that user:
+
+   ```bash
+   sudo chown 1001:1001 /home/padriano/share
+   ```
+
 3. Bring the full stack up:
 
    ```bash
@@ -127,7 +133,7 @@ docker inspect forgejo
 
 ### samba
 
-- Shared directory on the host: `/home/padriano/share`
+- Shared directory on the host: `/home/padriano/share` — must be owned by `1001:1001` (the UID/GID the container uses internally); without this, the share mounts on the Mac but files cannot be written
 - Uses a macvlan network with static IP `192.168.1.247` — avoids port 445 conflict with the `timemachine` container
 - Config stored at `samba/smb.conf`; the `[Share]` section is the only exported share
 - Avahi service file at `samba/avahi-smb.service` advertises the share for Finder sidebar discovery (installed to `/etc/avahi/services/samba.service` on the host)

samba/smb.conf

@@ -45,3 +45,5 @@
   directory mask = 0775
   inherit permissions = no
   valid users = samba
+  force user = samba
+  force group = samba