refactor: sqlc vs raw SQL — hybrid approach (R3)

Deleted 8 genuinely unused sqlc queries (no inline equivalent):
- UpsertCurrentRelationship, ListEntitiesCapped, ListEntityStatus,
  UpdateSignalState, InsertClassification, InsertFeedback, InsertSkill,
  UpsertCurrentRelationship — all had zero call sites.

Migrated 9 inline raw SQL sites to use sqlc queries:
- GetOntology (impl.go): ListEntityTypes, ListRelationshipTypes,
  ListLifecycleDefs — replaces 3 raw pool.Query blocks with typed sqlcgen
  calls, eliminating manual row scanning.
- EndRelationship (phase3.go): EndCurrentRelationship — replaces tx.Exec
  with sqlcgen.New(tx).EndCurrentRelationship.
- checkPrecondition (impl.go): GetEntityStatus — replaces tx.QueryRow +
  manual Scan with sqlcgen.New(tx).GetEntityStatus.
- GetEntityRelations (impl.go): ListEntityRelations — replaces raw pool.Query
  + scanRelationships helper (now deleted).
- GetGraph (impl.go): ListGraphEdges — replaces raw pool.Query +
  scanRelationships.
- resolveEntityID (impl.go): GetEntityBySlug/GetEntityByID — replaces
  raw pool.QueryRow + Scan.
- createApproval (mcp/server.go): InsertApproval — replaces raw pool.Exec
  with sqlcgen.InsertApproval.

Deleted scanRelationships helper (was only used by the two migrated
graph queries above).

Regenerated sqlcgen — also picks up stale model updates (AgentSession,
SessionPlanStep, SessionQuestion, etc. from recent migrations).

Documented the carve-out in .agents/dev/CONTRIBUTING.md §SQL conventions:
sqlc is the default; raw pool.Query/Exec is reserved for LISTEN/NOTIFY,
dynamic WHERE builders, blast_radius(), and COPY.

go vet, build, httpapi/mcp/db tests all pass. -383/+170 lines.

internal/db/sqlcgen/entities.sql.go

@@ -177,43 +177,6 @@ func (q *Queries) ListEntities(ctx context.Context, arg ListEntitiesParams) ([]E
 	return items, nil
 }
 
-const listEntitiesCapped = `-- name: ListEntitiesCapped :many
-SELECT e.id, e.slug, e.type, e.name, e.state, e.attributes, e.maintenance_until, e.version, e.created_at, e.updated_at, e.enrolled_at, e.enrolled_by FROM entities e ORDER BY e.slug LIMIT $1
-`
-
-func (q *Queries) ListEntitiesCapped(ctx context.Context, limit int32) ([]Entity, error) {
-	rows, err := q.db.Query(ctx, listEntitiesCapped, limit)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close()
-	var items []Entity
-	for rows.Next() {
-		var i Entity
-		if err := rows.Scan(
-			&i.ID,
-			&i.Slug,
-			&i.Type,
-			&i.Name,
-			&i.State,
-			&i.Attributes,
-			&i.MaintenanceUntil,
-			&i.Version,
-			&i.CreatedAt,
-			&i.UpdatedAt,
-			&i.EnrolledAt,
-			&i.EnrolledBy,
-		); err != nil {
-			return nil, err
-		}
-		items = append(items, i)
-	}
-	if err := rows.Err(); err != nil {
-		return nil, err
-	}
-	return items, nil
-}
-
 const updateEntity = `-- name: UpdateEntity :one
 UPDATE entities SET
     name = COALESCE($1, name),