fix: set uid/gid for directory entries in cas_getattr and add sudo to README

[haoren3696]

Summary

• Fix ownership of root and Tree (directory) entries in cas_getattr — previously missing st_uid/st_gid assignment caused mount points and all subdirectories to appear owned by root:root instead of the calling user.
• Add missing sudo to the dnf install command in the openEuler build section of README.

Error related to ownership issue:

[user1@localhost ContextFS]$ ./start.sh .
mount=/tmp/agentvfs-1001/ContextFS/mount
next: cd /tmp/agentvfs-1001/ContextFS/mount && claude   # or: codex
[user1@localhost ContextFS]$ cd /tmp/agentvfs-1001/ContextFS/mount
[user1@localhost mount]$ git status
fatal: detected dubious ownership in repository at '/tmp/agentvfs-1001/ContextFS/mount'
To add an exception for this directory, call:

        git config --global --add safe.directory /tmp/agentvfs-1001/ContextFS/mount
[user1@localhost mount]$ ls -al /tmp/agentvfs-1001/ContextFS/mount
total 0
drwxr-xr-x. 2 root  root      0 Jan  1  1970 .
drwx------. 5 user1 user1   180 May 24 18:04 ..
drwxr-xr-x. 2 root  root      0 Jan  1  1970 benchmarks
drwxr-xr-x. 2 root  root      0 Jan  1  1970 build
drwxr-xr-x. 2 root  root      0 Jan  1  1970 cmake
-rw-r--r--. 1 user1 user1 28004 Jan  1  1970 CMakeLists.txt
drwxr-xr-x. 2 root  root      0 Jan  1  1970 demo
drwxr-xr-x. 2 root  root      0 Jan  1  1970 docs
drwxr-xr-x. 2 root  root      0 Jan  1  1970 .git
drwxr-xr-x. 2 root  root      0 Jan  1  1970 .github
-rw-r--r--. 1 user1 user1   506 Jan  1  1970 .gitignore
drwxr-xr-x. 2 root  root      0 Jan  1  1970 include
-rw-r--r--. 1 user1 user1  3411 Jan  1  1970 install.ps1
-rwxr-xr-x. 1 user1 user1  5018 Jan  1  1970 install.sh
drwxr-xr-x. 2 root  root      0 Jan  1  1970 lib
-rw-r--r--. 1 user1 user1 11350 Jan  1  1970 LICENSE
-rw-r--r--. 1 user1 user1  4957 Jan  1  1970 README.md
drwxr-xr-x. 2 root  root      0 Jan  1  1970 scripts
drwxr-xr-x. 2 root  root      0 Jan  1  1970 src
-rwxr-xr-x. 1 user1 user1  5503 Jan  1  1970 start.sh
drwxr-xr-x. 2 root  root      0 Jan  1  1970 tests
[user1@localhost mount]$ ls -al /home/user1/ContextFS
total 128
drwxr-xr-x. 14 user1 user1  4096 May 24 18:02 .
drwx------.  5 user1 user1  4096 May 24 18:04 ..
drwxr-xr-x.  3 user1 user1  4096 May 24 18:02 benchmarks
drwxr-xr-x.  3 user1 user1  4096 May 24 18:03 build
drwxr-xr-x.  2 user1 user1  4096 May 24 18:02 cmake
-rw-r--r--.  1 user1 user1 28004 May 24 18:02 CMakeLists.txt
drwxr-xr-x.  4 user1 user1  4096 May 24 18:02 demo
drwxr-xr-x.  4 user1 user1  4096 May 24 18:02 docs
drwxr-xr-x.  8 user1 user1  4096 May 24 18:02 .git
drwxr-xr-x.  3 user1 user1  4096 May 24 18:02 .github
-rw-r--r--.  1 user1 user1   506 May 24 18:02 .gitignore
drwxr-xr-x.  3 user1 user1  4096 May 24 18:02 include
-rw-r--r--.  1 user1 user1  3411 May 24 18:02 install.ps1
-rwxr-xr-x.  1 user1 user1  5018 May 24 18:02 install.sh
drwxr-xr-x.  2 user1 user1  4096 May 24 18:02 lib
-rw-r--r--.  1 user1 user1 11350 May 24 18:02 LICENSE
-rw-r--r--.  1 user1 user1  4957 May 24 18:02 README.md
drwxr-xr-x.  2 user1 user1  4096 May 24 18:02 scripts
drwxr-xr-x.  4 user1 user1  4096 May 24 18:02 src
-rwxr-xr-x.  1 user1 user1  5503 May 24 18:02 start.sh
drwxr-xr-x.  3 user1 user1  4096 May 24 18:02 tests

Steps to reproduce the ownership problem

useradd -m -G wheel user1
passwd user1
su user1
cd ~/
git clone https://github.com/thustorage/ContextFS.git
cd ContextFS/
cmake -B build && cmake --build build -j
sudo cmake --install build
./start.sh .
cd /tmp/agentvfs-1001/ContextFS/mount
git status
ls -al /tmp/agentvfs-1001/ContextFS/mount
ls -al /home/user1/ContextFS

[Zhihaoi]

LGTM