Install deploy and administer refinement

[shainaraskas]

Redo of #3065

Strategy: Each deployment type's docs are split into a deploy flow (install through first production-ready deployment) and an admin section (ongoing operations). Key pages appear in both sections (# BOTH PHASES). Cross-cutting admin content (security, monitoring, backups, upgrades, etc.) stays in shared sections, organized into three visual zones separated by dividers. Production readiness checklists at the end of each deploy flow bridge users into the admin and cross-cutting sections they need.

strategy deep dive

TODOs:

• Write production readiness checklists for each deployment type (highest priority — the strategy doesn't work without them)
• Update deploy-manage/index.md to surface both deployment-specific and cross-cutting admin sections
• Fill in the Connect to Elasticsearch and Access Elasticsearch placeholder pages