feat: Phase 2 — ports package, secrets port move, postgres adapter move

Problem: the hexagon's Phase 2 (plans/2026-08-15-hexagonal-architecture.md)
must give the use-cases-to-be their contract surface: driven-port
interfaces, test fakes, the secrets interface moved into core, and the
postgres package inside the adapters tree — before the first vertical
slice (Phase 3) can wire a composition root.

Change:
- internal/core/ports: full driven-port catalog per plan §3.3 —
  repositories as transaction-scoped aggregates whose inputs carry
  derived checks, audit, and events (§3.6), plus CommandExecutor,
  TargetResolver, Checker, Secrets, EventPublisher, Provisioner.
  Port-local payload types (Event, AuditEntry, CheckDef, KnowledgeEntry,
  ExecResult) keep signatures off infrastructure; TypeTree aliases
  internal/ontology (pure over domain) until checkdefaults is absorbed.
  ReadModels intentionally not declared yet — it materializes with the
  Phase 3 slice and grows as report handlers rewire.
- secrets.Backend is now an alias of ports.Secrets; implementations
  (Infisical, SOPS, Manager) unchanged. mcp's local secretBackend
  subset is deleted; tool constructors take ports.Secrets.
- internal/db → internal/adapters/postgres (mechanical import rewrite;
  package identifier stays db until the Phase 3 repository split).
  sqlc.yaml, Makefile, golangci exclusions, and docs follow the move;
  make generate-check verified.
- internal/adapters/ssh: Executor implements ports.CommandExecutor over
  the actuator dial pool + RunStreaming (10-min default timeout carried
  over from the httpapi path).
- internal/adapters/remote: Resolver implements ports.TargetResolver
  delegating to internal/remote (still pool-based; drops onto
  ports.EntityRepository when repositories land in Phase 3 — documented
  transitional import).
- internal/core/ports/portstest: importable fakes — in-memory
  EntityRepo (with check-then-act SetState, side-effect recording),
  RecordingExecutor, FakeChecker, SpyPublisher; port-satisfaction
  guards; tests.

Risk: ports are declared ahead of implementations — signatures firm up
per phase as slices land (documented in the package doc); the
remote→postgres transitional import is explicit and dissolves in
Phase 3.

Verification: go vet, make test (race, 19 packages), generate-check,
golangci on core+adapters — 0 issues; full-repo baseline down
365→344.

internal/core/ports/events.go

@@ -0,0 +1,45 @@
+package ports
+
+import (
+	"context"
+	"time"
+
+	"github.com/dtoro/oikos/internal/core/domain"
+)
+
+// Event is a domain occurrence worth publishing (SSE + events table). The
+// events adapter maps it to the persistence/SSE shapes.
+type Event struct {
+	Type     string // e.g. "execution.completed", "health.changed"
+	Severity string // "info", "warning", "critical"
+	Source   string // "api", "mcp", "scheduler", "webhook"
+	EntityID domain.UUID
+	Data     map[string]any
+	Ts       time.Time
+}
+
+// EventPublisher fans events out to subscribers and persists them. The
+// events adapter owns the SSE broker, the events table, and the dedicated
+// LISTEN/NOTIFY connection.
+type EventPublisher interface {
+	Publish(ctx context.Context, event Event) error
+}
+
+// AuditEntry is an append-only audit-log record.
+type AuditEntry struct {
+	ActorType  string // "agent", "operator", "system"
+	ActorLabel string
+	Action     string
+	EntityID   domain.UUID
+	Details    map[string]any
+	Ts         time.Time
+}
+
+// AuditRepository appends audit records and events. Entries are usually
+// carried inside other repositories' input structs so they commit in the
+// same transaction (§3.6 of the plan); the standalone methods serve
+// read-path actions that audit without another aggregate write.
+type AuditRepository interface {
+	AppendAudit(ctx context.Context, entries []AuditEntry) error
+	AppendEvent(ctx context.Context, events []Event) error
+}