refactor(quota): modularize quota providers and add docs map (#427)

* refactor(quota): migrate server quota providers to modular registry architecture

* docs: add quota module documentation

Explain the quota module purpose and runtime signals.
List entrypoints, provider registry, and response shape.
Outline steps to add a new provider and testing commands.

packages/web/server/lib/quota/utils/index.js

@@ -0,0 +1,10 @@
+/**
+ * Quota Utilities
+ *
+ * Shared utility functions for quota calculations and formatting.
+ * @module quota/utils
+ */
+
+export * from './auth.js';
+export * from './transformers.js';
+export * from './formatters.js';