milestone 4h: remove x day old files over X MB (temporary sharingservice for big files)

added 'cleanup_big_files' function to manyfold.sh.

Demo:

```
$ docker run xrforge
...
````

create a 10MB dummy_file.txt (and rewind date some years):

```
$ docker exec xrforge 'dd if=/dev/zero of=/mnt/models/dummy_file.txt bs=1M count=10'
10+0 records in
10+0 records out
10485760 bytes (10.0MB) copied, 0.005670 seconds, 1.7GB/s

$ touch -d "2021-01-01" /mnt/models/dummy_file.txt
$
```

Now when setting maxmb's to `5` and maxdays to `5`, we can see in the logs
that it gets deleted:

```
[/bin/infinite cleanup_big_files /mnt/models 5 5] Fri Aug  1 14:19:08 UTC 2025 executing
deleting: /mnt/models/dummy_file.txt
```

This behaviour is default, and can be disabled by docker environment-flag `NO_DISABLEBIGFILES`

manyfold/cli/manyfold.sh

@@ -38,7 +38,22 @@ overlayfs(){
   test -d /manyfold || return 0; # nothing to override 
   echocolor "[$APPNAME]" "applying filesystem overlay"
   cd /manyfold
-  rsync -ravuzi * /.
+  rsync -rvzi * /.
+}
+
+# cron-like function using sleep (./manifold.sh infinite 3600 zip -r /backup.zip /)
+infinite(){
+  trap 'echocolor "/bin/infinite $*: process ended..infinite does not care.."; sleep 2s' INT
+  interval=$1
+  shift
+  loop(){ 
+    echocolor "[/bin/infinite $*]" "$(date) started"
+    while sleep ${interval}; do 
+      echocolor "[/bin/infinite $*]" "$(date) executing"
+      "$@" 
+    done; 
+  }
+  loop "$@"
 }
 
 db(){
@@ -111,6 +126,28 @@ rename_app(){
   sed -i 's|powered_by_html:.*|powered_by_html: Powered by <a href="https://forgejo.isvery.ninja/coderofsalvation/xrforge">XR Forge</a>, <a href="https://manifold.app" target="_blank">Manyfold</a>, <a href="https://xrfragment.org">XR Fragments</a> and <a href="https://nixos.org" target="_blank">NIX</a>|g' /usr/src/app/config/locales/*.yml
 }
 
+cleanup_big_files(){
+  local DIR=$1
+  local MAX_DAYS=$2
+  local MAX_MB=$3
+  test -n "$MAX_DAYS" && test -n "$MAX_MB" && {
+    find "$DIR" -type f -mtime +"$MAX_DAYS" -size +$(( $MAX_MB * 1024 ))k | while read file; do 
+      echo "deleting: $file"
+      rm "$file"
+    done 
+  }
+}
+
+delete_big_files(){
+  #./manyfold infinite 86400 cleanup_big_files /mnt/models 5 5 & # 5 days for files over 5MB (5 in 2025, 6 in 2026 e.g. ?)
+  # check every day to delete files older than 5 days and >5mb (5mb in 2025, 6mb in 2026 e.g.)
+  test -z "$NO_DELETEBIGFILES" && {
+    intervalSec=86400 # = 1 day
+    maxMB=$(( $(date +%Y) - 2020 ))
+    $0 infinite 5 cleanup_big_files /mnt/models $intervalSec $maxMB & 
+  }
+}
+
 # The new entrypoint of the docker 
 boot(){
   echocolor "[$APPNAME]" "booting..."
@@ -121,6 +158,8 @@ boot(){
   set_modelpath
   rclone_mount
   set_upload_path
+  delete_big_files
+
   exec "$@" # exec prevents error 's6-overlay-suexec: fatal: can only run as pid 1'
 }