feat: Phase 9 gaps closed — ApprovalService.Decide convergence, execlog fold, execworker poller

- ApprovalService (core/app/approval.go) + ApprovalRepo (postgres adapter) with
  full decide transaction: HMAC token verify, approval flip, execution un-gate,
  session-scoped window keys (+session suffix matching GovernanceStore gate),
  nomos session flip, audit+event on failure abort. httpapi DecideApproval now
  a thin presenter delegating to the service. ListPending payload format fixed
  (json.Unmarshal not raw-wrap).
- execlog folded into postgres adapter: internal/execlog deleted, NewExecutionLog
  / ReadExecutionLog live in the db package, callers updated (mcp, httpapi).
- execworker poller over ExecutionService.DispatchQueued: advisory lock leak
  fixed (defer/recover per execution), correlation_id preserved via Finalize
  event emission (ExecRunRepo.Finalize now emits execution.{status} with
  correlation_id from the row).
- Phase 8 session export-rename completed: Store, New, and all 53 methods
  exported; cmd/nomos/ agent.go fixed to use session.PendingContinuation etc.
- Coverage gates: ExecutionService.Submit 93.1%, PolicyService.Decide 100%.
- Plans index updated, VERSION bumped to 0.36.0.

internal/httpapi/execution_logs.go

@@ -6,7 +6,7 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/dtoro/oikos/internal/execlog"
+	"github.com/dtoro/oikos/internal/adapters/postgres"
 	"github.com/go-chi/chi/v5"
 	"github.com/google/uuid"
 )
@@ -34,7 +34,7 @@ func (s *Server) serveExecutionLogs(w http.ResponseWriter, req *http.Request) {
 		}
 	}
 
-	chunks, err := execlog.Read(ctx, s.pool, execID, limit)
+	chunks, err := db.ReadExecutionLog(ctx, s.pool, execID, limit)
 	if err != nil {
 		writeProblem(w, req, http.StatusInternalServerError, "query failed", err.Error())
 		return