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/domains/knowledge/schema.md

@@ -0,0 +1,48 @@
+# Knowledge domain — schema
+
+The knowledge domain is the durable, authoritative current-state documentation of the homelab: one
+page per node and per cross-cutting system, synthesized from live state and evidence. It answers
+"what exists and how does it work right now."
+
+It follows the [LLM Wiki layer model](../../shared/llm-wiki.md) and the
+[writing-style](../../shared/writing-style.md) and [page-templates](../../shared/page-templates.md)
+rules.
+
+## The narrative / substrate split
+
+The knowledge wiki is **narrative**. It sits alongside a **machine-readable substrate** that it
+describes but never contains. The split is load-bearing: several programs read the substrate at
+fixed paths, so the wiki reorganization never moves it.
+
+| Layer | Location | Consumed by |
+|-------|----------|-------------|
+| Substrate — source of truth | `inventory.yaml` (root) | MCP server, `homelab` CLI, `oikos/` scheduler/drift/relations/gen-topology |
+| Substrate — generated host records | `hosts/*.yaml` (root) | `mcp/server.py` (`HOSTS_DIR`), `bin/homelab`; written by `mcp/build_host_files.py` |
+| Substrate — kernel + context cards | `oikos/` (code, `oikos/cards/`, `oikos/state.json`) | MCP `explain`, scheduler |
+| Narrative — synthesized wiki | `knowledge/wiki/{hosts,containers,vms,infrastructure}/` | humans, agents via MCP `get_page` / `search_docs` |
+| Evidence — immutable sources | `knowledge/sources/`, `investigations/` | synthesis into wiki pages |
+
+## Wiki pages
+
+- **Node pages** (`knowledge/wiki/containers/<id>-<name>.md`, `.../vms/<id>-<name>.md`,
+  `.../hosts/<name>.md`) follow the container/host template in
+  [page-templates.md](../../shared/page-templates.md): opening definition, `## At a glance`,
+  `## Role`, service/port map, storage, auto-deploy, `## Related`, `## Changelog`.
+- **Cross-cutting pages** (`knowledge/wiki/infrastructure/<topic>.md`) follow the cross-cutting
+  template: `## Why`, `## Components`, `## How to apply`, `## Gotchas`, `## Related`, `## Changelog`.
+- Each `inventory.yaml` host entry carries a `doc_page:` field pointing at its narrative page.
+  Changing where a page lives means updating that field (read by `bin/homelab`).
+
+## The two logs
+
+- The per-page **`## Changelog`** records infrastructure changes and is machine-parsed
+  (`get_changelog`, the Oikos ledger). Keep the `### YYYY-MM-DD — title` shape.
+- **`knowledge/log.md`** is append-only and records *documentation-maintenance* operations only
+  (restructures, source ingests, lint sweeps): `## [YYYY-MM-DD] <op> | <summary>`. It never
+  duplicates the Oikos change ledger (`oikos/ledger.py`).
+
+## Same-session update rule
+
+A change to a node updates every page that references it in the same session — the node page, the
+section `README.md` table, the root `README.md`, the Caddy/DNS/ingress pages, the host page, and
+`inventory.yaml`. See [page-templates.md](../../shared/page-templates.md#same-session-update-rule).