feat(core): Add @file syntax for reading URIs from file

[scottsen]

Problem

Currently, batch processing requires piping through stdin:

cat domains.txt | sed 's/^/ssl:\/\//' | reveal --stdin --check

This is awkward when:

• You have a prepared list of URIs
• You want to re-run the same check multiple times
• You're working in environments where piping is cumbersome

Proposed Solution

Add @file syntax to read URIs directly from a file:

# File contains one URI per line:
# ssl://domain1.com
# ssl://domain2.com
# ssl://domain3.com

reveal @domains.txt --check

Or for the ssl:// adapter specifically:

# File contains just domains (one per line):
# domain1.com
# domain2.com

reveal ssl://@domains.txt --check

Prior Art

• curl uses @filename for reading request bodies
• jq uses --slurpfile
• Many CLI tools support - for stdin, @file for file input

Benefits

1. Simpler commands for repeated audits
2. Easier to version control domain lists
3. Works better in scripts without complex piping
4. Natural extension of existing --stdin behavior