ci: add ThreatCrush security scan

[ralyodio]

Installs threatcrush-scan@1.1.0 from the sh1pt Actions Store.

Scans pull requests for hardcoded credentials, injection, SSRF, unsafe deserialisation, XXE and dependency tampering. Findings go to the Security tab as SARIF and to a PR comment; snippets are redacted.

Report-only. It will not fail a pull request.

🤖 Generated with Claude Code

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.

[github-actions]

ThreatCrush Security Scan

19 finding(s)

HIGH/CRITICAL: 19

Severity	Rule	Location
HIGH	threatcrush-generic-secret	examples/config-demo.js:29
HIGH	threatcrush-generic-secret	examples/distrokid-demo.js:25
HIGH	threatcrush-generic-secret	test/cli.test.js:24
HIGH	threatcrush-generic-secret	test/config-generator.test.js:39
HIGH	threatcrush-generic-secret	test/config-generator.test.js:87
HIGH	threatcrush-generic-secret	test/config-generator.test.js:150
HIGH	threatcrush-generic-secret	test/config-generator.test.js:161
HIGH	threatcrush-generic-secret	test/distrokid-client.test.js:42
HIGH	threatcrush-generic-secret	test/distrokid-client.test.js:62
HIGH	threatcrush-generic-secret	test/distrokid-client.test.js:71
HIGH	threatcrush-generic-secret	test/distrokid-client.test.js:83
HIGH	threatcrush-generic-secret	test/distrokid-client.test.js:96
HIGH	threatcrush-generic-secret	test/distrokid-client.test.js:106
HIGH	threatcrush-generic-secret	test/distrokid-form-filler.test.js:8
HIGH	threatcrush-generic-secret	test/distrokid-publisher.test.js:25
HIGH	threatcrush-generic-secret	test/distrokid-publisher.test.js:48
HIGH	threatcrush-generic-secret	test/distrokid-publisher.test.js:62
HIGH	threatcrush-generic-secret	test/fuga-client.test.js:10
HIGH	threatcrush-generic-secret	test/tunecore-client.test.js:10

Snippets are redacted; ThreatCrush never prints matched credential material.