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- delete: 9 superseded Python kernel files, ledger/, mcp/build_host_files.py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

migrations/011_knowledge_search.up.sql

@@ -0,0 +1,4 @@
+ALTER TABLE knowledge_entities ADD COLUMN IF NOT EXISTS search tsvector
+  GENERATED ALWAYS AS (to_tsvector('english', COALESCE(title, '') || ' ' || COALESCE(content, ''))) STORED;
+
+CREATE INDEX IF NOT EXISTS idx_knowledge_search ON knowledge_entities USING GIN(search);