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- delete: 9 superseded Python kernel files, ledger/, mcp/build_host_files.py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

internal/httpapi/phase3.go

@@ -1738,16 +1738,6 @@ func float32Ptr(f float32) *float32 {
 	return &f
 }
 
-// ─── Knowledge (stubs — tables don't exist yet) ────────────────────────
-
-func (s *Server) SearchKnowledge(ctx context.Context, request gen.SearchKnowledgeRequestObject) (gen.SearchKnowledgeResponseObject, error) {
-	return nil, errNotImplemented
-}
-
-func (s *Server) GetEntityKnowledge(ctx context.Context, request gen.GetEntityKnowledgeRequestObject) (gen.GetEntityKnowledgeResponseObject, error) {
-	return nil, errNotImplemented
-}
-
 // ─── Agent Activity (stub) ─────────────────────────────────────────────
 
 func (s *Server) QueryAgentActivity(ctx context.Context, request gen.QueryAgentActivityRequestObject) (gen.QueryAgentActivityResponseObject, error) {