feat(strategy): add nexus-spatial-discovery runbook to NEXUS roster

[sunilkumarvalmiki]

Add the nexus-spatial-discovery runbook to the NEXUS roster, closing the gap between the existing examples/nexus-spatial-discovery.md and strategy/runbooks.json.

What this PR does

Adds a new runbook entry for nexus-spatial-discovery to strategy/runbooks.json, bringing the roster from 4 to 5 runbooks and agent slug references from 64 to 72.

Files

• strategy/runbooks.json (30 lines added, 1 entry appended)

Runbook details

• slug: nexus-spatial-discovery
• title: Nexus Spatial Discovery
• mode: NEXUS-Sprint (8 agents, 1-2 weeks)
• doc: examples/nexus-spatial-discovery.md (already exists)
• roster: Discovery Core group (product-trend-researcher, design-ux-researcher, engineering-backend-architect, design-brand-guardian) + Go-to-Market & Delivery group (marketing-growth-hacker, support-support-responder, project-management-project-shepherd, xr-interface-architect)

Checklist

• Template: one file change only.
• Frontmatter: N/A (JSON runbook).
• Examples: agents listed match the existing nexus-spatial-discovery.md.
• Tested locally: scripts/check-divisions.sh PASSED (18 divisions); scripts/check-tools.sh PASSED (16 tools); scripts/check-runbooks.sh PASSED (5 runbooks, 72 agent slug references).
• Proofread: all agent slug references resolve to real agent files.

Evidence

• scripts/check-divisions.sh: PASSED (18 divisions consistent)
• scripts/check-tools.sh: PASSED (16 tools consistent)
• scripts/check-runbooks.sh: PASSED (5 runbooks, 72 agent slug references)
• JSON validation: OK 5 runbooks
• CRLF check: no CRLF detected