db as source of truth: wiki→seeds, archive old artifacts, knowledge ingestion

- Migrations 010 (content_hash) + 011 (search tsvector column)
- new: internal/knowledge/seed.go — knowledge seed ingest engine
- new: internal/httpapi/knowledge.go — SearchKnowledge + GetEntityKnowledge
- wire knowledge ingest into oikos seed pipeline
- convert all 36 wiki docs + 6 investigations + 12 runbooks → seeds/knowledge.yaml
- archive: knowledge/wiki/→archive/, oikos/cards/→archive/, .hermes/plans/→archive/
- delete: 9 superseded Python kernel files, ledger/, mcp/build_host_files.py
- remove empty knowledge/ directory tree

archive/knowledge/hosts/index.md

@@ -0,0 +1,9 @@
+# Hosts
+
+The two Proxmox VE nodes that run the fleet. Narrative pages; the machine-readable host records are
+the generated `hosts/*.yaml` files at the repo root.
+
+| Document | What it covers |
+|----------|----------------|
+| [hubris.md](hubris.md) | Primary PVE node (GMKtec NucBox M6 Ultra, `192.168.8.77`) — runs most LXCs plus the VMs. |
+| [strong.md](strong.md) | Secondary PVE node / cluster member (`192.168.178.181`) — hosts the LXCs migrated from hubris. |