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>

AGENTS.md

@@ -5,10 +5,19 @@ context is in this checkout at `/opt/homelab-context/`. This file is the entry
 point. Read it once at start, then keep working.
 
 The operating model — OODA loop, risk classes, approval rules, the ontology,
-and node lifecycle — is defined in [OIKOS.md](OIKOS.md). Before any mutation,
+and node lifecycle — is defined in [OIKOS.md](.agents/OIKOS.md). Before any mutation,
 classify the action against `oikos/policy.yaml`; when the class requires
 approval, stop and ask the operator.
 
+Agent-facing instruction is separated from human content under `.agents/`:
+`.agents/shared/` holds the conventions every agent applies
+([writing-style](.agents/shared/writing-style.md), [caveman](.agents/shared/caveman.md),
+[page-templates](.agents/shared/page-templates.md), [llm-wiki](.agents/shared/llm-wiki.md)), and
+`.agents/domains/` holds the per-domain schemas
+([knowledge](.agents/domains/knowledge/schema.md), [operations](.agents/domains/operations/schema.md)).
+The narrative wiki lives under `knowledge/wiki/`; the machine-readable substrate
+(`inventory.yaml`, `hosts/*.yaml`, `oikos/`) stays at the repo root.
+
 ## 1. Who you are
 
 Run `hostname` (Linux) or `scutil --get LocalHostName` (macOS), then read:
@@ -102,7 +111,7 @@ Grep is fine for browsing or when MCP is unreachable.
 
 ## 6. Communication mode
 
-Read and apply `/opt/homelab-context/CAVEMAN.md` (if present). It defines the lab's
+Read and apply `/opt/homelab-context/.agents/shared/caveman.md` (if present). It defines the lab's
 terse-communication standard — drop filler, keep substance, use fragments.
 
 ## 7. Auto-setup mechanism