feat: add immutable cognitive event store, live streams and event explorer

Phase 3. Events are the append-only record of everything a mind does
(ADR-0002). pkg/events defines the closed type vocabulary, categories,
evidence references and the observation payload with explicit trust
levels. The store validates and appends inside the caller's transaction,
publishes to a bounded fan-out bus only after commit, queries by seq
cursor with type/category/source/salience/confidence/time/search
filters, and walks provenance: cause, parents, children, cited evidence,
derived events and correlation groups. Durable per-consumer cursors never
move backwards.

Server-Sent Events streams (per mind and global) subscribe before
replaying history after Last-Event-ID so nothing is missed, apply the
same filter vocabulary live, and heartbeat. Operators can inject
observations tagged with operator trust for demos and tests.

UI: live thought stream with filters and paging, forensic event page
with causal chain and evidence navigation, dashboard important events.
Personality and status changes now leave operator_action events in the
mind's own history. CLI: event inspect/list/tail, observe.

internal/api/api_test.go

@@ -14,6 +14,7 @@ import (
 	"github.com/andydixon/noema/internal/audit"
 	"github.com/andydixon/noema/internal/auth"
 	"github.com/andydixon/noema/internal/config"
+	evstore "github.com/andydixon/noema/internal/events"
 	"github.com/andydixon/noema/internal/minds"
 	"github.com/andydixon/noema/internal/observability"
 	"github.com/andydixon/noema/internal/storage"
@@ -27,7 +28,7 @@ func testServer(t *testing.T) (*httptest.Server, string) {
 	cfg.DatabaseURL = "postgres://test"
 	log := slog.New(slog.DiscardHandler)
 	deps := app.Deps{Config: cfg, Log: log, DB: pool, Auth: auth.NewService(pool, time.Hour, 2*time.Hour),
-		Audit: audit.New(pool, log), Metrics: observability.NewMetrics(), Minds: minds.NewStore(pool), Migrations: migrations.FS, Started: time.Now()}
+		Audit: audit.New(pool, log), Metrics: observability.NewMetrics(), Minds: minds.NewStore(pool), Events: evstore.NewStore(pool, evstore.NewBus(50), nil), Migrations: migrations.FS, Started: time.Now()}
 	ctx := context.Background()
 	u, err := deps.Auth.CreateUser(ctx, "admin", "administrator-pass", auth.RoleAdministrator)
 	if err != nil {