feat: add configuration, logging, metrics, scheduler and storage foundation

- config: defaults -> JSON file -> NOEMA_* env with validation and redaction
- observability: slog with secret-redacting handler; Prometheus registry with
  the metric set from the plan (events, workspace, memory, LLM, tools, queues)
- scheduler: supervised Group and bounded Pool so no goroutine is unowned
- storage: pgx pool with statement timeout, embedded migration runner
  (advisory lock, checksums, up/down/status), per-test schema helper
- migrations/0001: append-only guard trigger, users, sessions, api tokens,
  recovery codes, audit log, settings
- pkg/ids: UUIDv7 with monotonic counter

migrations/embed.go

@@ -0,0 +1,11 @@
+// Package migrations embeds the SQL schema migrations applied by
+// internal/storage. Files are named NNNN_name.up.sql / NNNN_name.down.sql and
+// are never edited once applied anywhere.
+package migrations
+
+import "embed"
+
+// FS contains every migration file.
+//
+//go:embed *.sql
+var FS embed.FS