Add CITATION.cff for academic and security-research citation

[azurebeard]

Context

Academic papers, security blog posts with proper bibliographies, and research write-ups that reference Harbinger benefit from a Citation File Format (CFF) entry in the repo root. GitHub renders a "Cite this repository" widget on the About sidebar when CITATION.cff is present, and tools like Zotero, Mendeley, and cffconvert pick it up automatically.

Scope

Create a CITATION.cff file at the repository root following the CFF v1.2.0 schema. Minimum fields:

cff-version: 1.2.0
message: "If you use Harbinger in research, please cite it as below."
type: software
title: "Harbinger: AI-powered log pre-classifier for Microsoft Sentinel"
abstract: "Observe-only profiler that classifies syslog events with a local Ollama model and produces a per-source tier recommendation report for Microsoft Sentinel cost optimisation."
authors:
  - family-names: "Beard"
    given-names: "Ben"
    email: "ben@azurebeard.co.uk"
    affiliation: "AzureBeard"
repository-code: "https://github.com/azurebeard/harbinger"
url: "https://azurebeard.co.uk"
license: Apache-2.0
version: "1.0.1"
date-released: "2026-06-22"
keywords:
  - microsoft-sentinel
  - siem
  - log-classification
  - ollama
  - syslog
  - cost-optimization

Update version and date-released to match the latest release at the time of merge.

Acceptance criteria

• CITATION.cff at repo root.
• Validates against the CFF schema. Validator: pip install cffconvert && cffconvert --validate -i CITATION.cff (zero output = valid).
• GitHub renders the "Cite this repository" widget on the About sidebar (verify after merge).
• Add a one-line entry in README.md's documentation index pointing at CITATION.cff.

Why this is a good first issue

One small new file. Demonstrates the OSS-discoverability pattern. Zero risk of breaking anything.