docs: adopt wiki-hq conventions + separate agent instructions (phases 1-2)

Problem: the narrative docs lacked an enforceable style standard, and
agent-facing instruction (OIKOS/CAVEMAN/CONTRIBUTING) was interleaved with
human content at the repo root.

Change:
- Add .agents/shared/{writing-style,llm-wiki}.md — a lint-checkable prose
  standard (with an imperative-voice exception for runbooks/recipes) and the
  sources/wiki/index/log layer model.
- Move CAVEMAN.md -> .agents/shared/caveman.md,
  CONTRIBUTING.md -> .agents/shared/page-templates.md,
  OIKOS.md -> .agents/OIKOS.md; leave thin root stubs so old links resolve.
- Add .agents/domains/{knowledge,operations}/schema.md; operations schema
  codifies "plans always live in plans/".
- Repoint live references (AGENTS, README, GLOSSARY, OIKOS) and fix OIKOS.md's
  internal relative links for its new depth.

Risk: none to the operational substrate — inventory.yaml, hosts/*.yaml,
oikos/, mcp/, secrets/, bin/ untouched (verified via git status).

Verification: relative-link check across .agents/ clean; substrate churn empty.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

GLOSSARY.md

@@ -18,7 +18,7 @@ Terms and abbreviations used throughout the homelab wiki.
 | **Mesh** | Overlay VPN for off-LAN connectivity. Netbird is current; Tailscale is legacy |
 | **Netbird** | Preferred mesh VPN. VPS hosts the management plane; all homelab nodes are members |
 | **OIDC** | OpenID Connect. Protocol used by Authentik for SSO login flows |
-| **Oikos** | Agent operating model (OIKOS.md). OODA loop, risk classes, policy, ontology |
+| **Oikos** | Agent operating model ([.agents/OIKOS.md](.agents/OIKOS.md)). OODA loop, risk classes, policy, ontology |
 | **PVE** | Proxmox Virtual Environment — the hypervisor on both hubris and strong |
 | **SOPS** | `sops` — Mozilla SOPS. Encrypts secrets with age keys so they live in the git repo |
 | **Strong** | Secondary Proxmox VE node. Cluster member 2 (hostname `strong`, nickname ludo/ludo-mini) |
@@ -30,4 +30,4 @@ Terms and abbreviations used throughout the homelab wiki.
 ## See also
 
 - [Infrastructure index](infrastructure/index.md) — cross-cutting systems each with their own doc page
-- [OIKOS operating model](OIKOS.md) — agent policy, risk classes, lifecycle
+- [OIKOS operating model](.agents/OIKOS.md) — agent policy, risk classes, lifecycle