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/knowledge.go

@@ -0,0 +1,54 @@
+package ports
+
+import (
+	"context"
+	"time"
+
+	"github.com/dtoro/oikos/internal/core/domain"
+)
+
+// KnowledgeEntry is a knowledge-base document/investigation/runbook.
+type KnowledgeEntry struct {
+	Slug      string
+	Title     string
+	Kind      string // "document", "investigation", "runbook"
+	Tags      []string
+	Content   string
+	About     []string // entity slugs the entry describes
+	UpdatedAt time.Time
+}
+
+// KnowledgeUpsertInput is the knowledge write: row + revision + about-edges
+// in one transaction.
+type KnowledgeUpsertInput struct {
+	Entry  KnowledgeEntry
+	Audit  []AuditEntry
+	Event  *Event
+}
+
+// KnowledgeRepository is the knowledge aggregate.
+type KnowledgeRepository interface {
+	Search(ctx context.Context, query string, limit int) ([]KnowledgeEntry, error)
+	GetContent(ctx context.Context, slug string) (KnowledgeEntry, error)
+	Revisions(ctx context.Context, slug string, limit int) ([]KnowledgeEntry, error)
+	Tags(ctx context.Context) (map[string]int, error)
+	Orphans(ctx context.Context, staleDays int) ([]KnowledgeEntry, error)
+	Duplicates(ctx context.Context, threshold float64) ([]KnowledgeEntry, error)
+
+	Upsert(ctx context.Context, input KnowledgeUpsertInput) (KnowledgeEntry, error)
+	Merge(ctx context.Context, targetSlug string, sourceSlugs []string) error
+	SoftDelete(ctx context.Context, slug string) error
+	Restore(ctx context.Context, slug string) error
+}
+
+// LearningRepository — patterns, feedback, skills (reads plus simple
+// upserts; no multi-aggregate transactions here).
+type LearningRepository interface {
+	ListFeedback(ctx context.Context, limit int) ([]domain.Pattern, error)
+	ListPatterns(ctx context.Context, limit int) ([]domain.Pattern, error)
+	ListSkills(ctx context.Context) ([]domain.Pattern, error)
+
+	UpsertPattern(ctx context.Context, pattern domain.Pattern) error
+	Validate(ctx context.Context, patternID domain.UUID) error
+	Quarantine(ctx context.Context, patternID domain.UUID, reason string) error
+}