docs(platform): reference cyber kill chain coverage map

[raylee-hawkins]

Summary:

• Adds pointer to canonical proof artifact.
• Does not duplicate the artifact.
• Does not promote runtime/signal/public-safe/production claims.
• Website untouched.

Validation:

• git diff --check
• No general platform README-specific validator found.

Claim boundary:

• Canonical artifact remains in hawkinsoperations-proof.
• This repo contributes workflow, case-packet, automation, and AI-support boundary truth and is not proof authority.
• No runtime-active, signal-observed, public-safe runtime, production-ready, autonomous SOC, AI-approved, or analyst-approved claim is promoted.

[raylee-hawkins]

Human governance review:

Reviewed the cross-repo Cyber Kill Chain pointer scope for platform.

Approved scope:

• README.md only

Confirmed:

• This PR adds a pointer to the canonical Cyber Kill Chain coverage artifact in hawkinsoperations-proof.
• It does not duplicate the artifact.
• It keeps platform as workflow, automation, and support-boundary contribution, not proof authority.
• It does not promote runtime, signal, public-safe runtime, production, autonomous, or disposition-authority claims.
• Website remains untouched.

This pointer is approved as reviewer navigation only.