Sigma detection-rule attribution and license notice

Imported Sigma rule definitions retain their original author fields and source
content. Each rule reference exposes its pinned source URL and the rule's author,
status, dates and SHA-256. Machine-readable attribution accompanies each rule in
data/detection-rules/<UUID>.json.

Source snapshot: https://github.com/anpa1200/sigma/tree/b249e9683190cffdcaf188ccbfb90bf4759844e1
Upstream project: https://github.com/SigmaHQ/sigma
License: Detection Rule License (DRL) 1.1
License text: https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md

Preserve the authors, source URI and license when sharing these rules. No rule is
warranted to be effective or suitable for a particular environment. Rules have
not been compiled against a backend or evaluated on live telemetry in this module.

This notice covers the imported Sigma definitions, not all other site content.