fix: Fix permissions for operating files and directories

[Nerahikada]

Description

This PR will fix permission issues (#2535, #3281, #3399) by making permissions as lax as possible when handling files and directories.
However, I know nothing about the possible (and dangerous) side effects of this change.

Further comments

Tested on Ubuntu 24.04.2 LTS and Go 1.23.0.
file0, dir0 is the file created before the change, file1, dir1 is the file created by the command line, and file2, dir2 is the file created by the modified filebrowser.

ubuntu@8d98ab8f6f40:~/filebrowser/working$ uname -a
Linux 8d98ab8f6f40 6.11.0-21-generic #21-Ubuntu SMP PREEMPT_DYNAMIC Wed Feb 19 16:50:40 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
ubuntu@8d98ab8f6f40:~/filebrowser/working$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=24.04
DISTRIB_CODENAME=noble
DISTRIB_DESCRIPTION="Ubuntu 24.04.2 LTS"
ubuntu@8d98ab8f6f40:~/filebrowser/working$ go version
go version go1.23.0 linux/amd64
ubuntu@8d98ab8f6f40:~/filebrowser/working$ ls -lha
total 64K
drwxrwxr-x 5 ubuntu ubuntu 4.0K Mar 31 19:29 .
drwxrwxr-x 1 ubuntu ubuntu 4.0K Mar 31 19:43 ..
drwxr-xr-x 2 ubuntu ubuntu 4.0K Mar 31 19:25 dir0
drwxrwxr-x 2 ubuntu ubuntu 4.0K Mar 31 19:27 dir1
drwxrwxr-x 2 ubuntu ubuntu 4.0K Mar 31 19:28 dir2
-rw-r--r-- 1 ubuntu ubuntu    0 Mar 31 19:25 file0
-rw-rw-r-- 1 ubuntu ubuntu    0 Mar 31 19:27 file1
-rw-rw-r-- 1 ubuntu ubuntu    0 Mar 31 19:29 file2
-rw------- 1 ubuntu ubuntu  64K Mar 31 19:28 filebrowser.db

[Nerahikada]

Why do people mention me without creating a PR with only two lines of changes?

[domme1908]

@o1egl could this be merged?

[str0ngb4d]

I could use this fix as well. Without it, it's difficult to use filebrowser to share files across OS users.

[o1egl]

Elevating permissions might be dangerous in some installations. I'd make it configurable, keeping current permissions as defaults

[hacdias]

This feature - it is not a fix, since it is working as intended - will not be published in the current form.

Just like @o1egl mentioned, if you want this, it needs to be optional. Please add a flag to change the default file and directory permissions instead.

[Nerahikada]

I'll close this because the maintainer is back