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- delete: 9 superseded Python kernel files, ledger/, mcp/build_host_files.py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/sources/index.md

@@ -0,0 +1,9 @@
+# Sources
+
+Immutable evidence the wiki synthesizes from. External reference docs live under `references/`;
+incident evidence lives in [`investigations/`](investigations/index.md) (written once at
+incident time, then linked from the changelogs of the nodes they implicate).
+
+| Slug | Reference | Summary |
+|------|-----------|---------|
+| cert-sync-and-traefik-config | [references/cert-sync-and-traefik-config.md](references/cert-sync-and-traefik-config.md) | VPS traefik config and the LAN↔VPS certificate mirror. |