docs(repo): scaffold documentation-first direction, add ADRs, templates, and archive legacy infra

[azunaVT]

Motivation

• Pivot the repository to a documentation-first, Proxmox-first homelab platform direction to replace the previous bare-metal Talos/PXE focus.
• Capture canonical architecture, decisions, inventories, runbooks, and a prioritized roadmap so execution is repeatable and reviewable.
• Standardize GitHub workflows by providing issue and PR templates and area README anchors for future work.

Description

• Add a top-level README.md that documents the Proxmox-first direction, repo structure, and reading path for initial work.
• Add a full docs scaffold under docs/ including architecture/, decisions/ (ADRs ADR-001..ADR-005), inventory/, roadmap/, runbooks/, and vision/ to capture design goals, TODOs, and milestones.
• Introduce GitHub templates in .github/ with issue templates (decision.yml, epic.yml, task.yml) and a pull_request_template.md to standardize planning and PRs.
• Create area README stubs for proxmox/, kubernetes/, argocd/, ai/, automation/, scripts/, and argocd/ to organize future implementation artifacts.
• Archive the legacy bare-metal/Talos Terraform and infra material into docs/archive/legacy-baremetal-talos-pxe/, remove the sensitive infra/live/prod/terraform.auto.tfvars, and replace it with a redacted example in the archive.

Testing

• No automated tests were run because this is a documentation and repository re-organization change.

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Codex Task