[Bug] --no-ext with a leading dot fails to exclude matching files

[equationzhao]

Describe the bug
--no-ext .txt should exclude a.txt, but it leaves it in the output.

To Reproduce

1. Build the current repository:

go build -o /tmp/g-bug-audit .

2. Create files with different extensions:

tmp=$(mktemp -d)
touch "$tmp/a.txt" "$tmp/b.csv" "$tmp/noext"

3. Exclude a leading-dot extension:

/tmp/g-bug-audit --no-config --disable-index --classic -A --byline --no-ext .txt "$tmp"
printf 'exit=%s tmp=%s\n' $? "$tmp"

4. Actual output:

a.txt
b.csv
noext
exit=0 tmp=/var/folders/1b/57vdxmgj7s1glqm6tbsw1frm0000gn/T/tmp.KVFkWQ4vdQ

5. Control check without the leading dot:

/tmp/g-bug-audit --no-config --disable-index --classic -A --byline --no-ext txt "$tmp"

Actual control output:

b.csv
noext
exit=0 tmp=/var/folders/1b/57vdxmgj7s1glqm6tbsw1frm0000gn/T/tmp.kC5Zi304XL

6. Expected output: a.txt should be excluded when the user passes .txt, or the CLI should reject the input with a clear validation error.

Screenshots
Not applicable.

Info (please complete the following information):

• OS: macOS darwin/arm64
• Version: v0.31.2, Go go1.26.1

Additional context
The extension exclusion filter appears to prepend . to the provided value. If the user already passed .txt, the effective suffix becomes ..txt.