model-usage: the vendor-neutral usage store (ADR 0054)

The home ADR 0050 left open for a usage reading. mesh-control is a CLI and
cannot consume events, so the store that keeps the current usage picture is a
MODULE — the audit-logger's sibling: it consumes `module.*.usage.*` and upserts
each reading into its own provisioned postgres store, latest per
(licence, consumer, period, metric), in the clear. One vendor-neutral table
holds BOTH grains; they differ only in `consumer` (the holding module for the
licence grain, the session for the finer one). The consumer creates its table
on startup and, as a restart-until-ready service, self-heals rather than
gating the apply on a run-once that must reach a provider over the overlay.

The vendor->row normalisation moves into the adapter, as ADR 0054 requires:
anthropic-manager (licence grain, utilization%) and anthropic-consumer (session
grain, token/cost) now emit already-normalised { rows: UsageRow[], raw } on
their existing keys, so the store stays vendor-blind.

Proven end to end by the mesh-lab model-usage bed (green): a usage event
emitted into the mesh is upserted at both grains, latest-per-key, in the clear.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

modules/model-usage/pg.d.ts

@@ -0,0 +1,15 @@
+// Ambient types for `pg` (node-postgres), which ships its types only via the separate `@types/pg`
+// package. Rather than pull that in at tsc time, this declares the exact slice model-usage uses —
+// the same precedent anthropic-manager sets for `tweetnacl-sealedbox-js` (a local ambient .d.ts,
+// listed in tsconfig `include`, default-imported). The real `pg` is installed into the module's
+// runtime image (package.json `dependencies`; novox/hq ADR 0052), so this types the code without
+// deciding what runs.
+declare module "pg" {
+  /** A lazily-connecting connection pool. Only the connection string, one query form, and end() are
+   *  used here. */
+  export class Pool {
+    constructor(config?: { connectionString?: string });
+    query(text: string, params?: unknown[]): Promise<{ rows: any[]; rowCount: number }>;
+    end(): Promise<void>;
+  }
+}