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- delete: 9 superseded Python kernel files, ledger/, mcp/build_host_files.py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/oikos-cards/cards/host-mac-mini.md

@@ -0,0 +1,17 @@
+# mac-mini (host:mac-mini)
+
+- kind: workstation
+- state: active
+- role: dev
+- address: 192.168.178.182 (mesh: netbird:mac-mini-234-17.netbird.selfhosted)
+- secrets: enrolled (age key present)
+
+## Blast radius
+- impacts: (none)
+- affected by: (none)
+
+## Safe actions
+- see the services this host runs for action-level risk classes
+
+## Recent changes
+- (none yet)