Add agent skill (SKILL.md + per-domain reference)

skills/rudder-web-sdk/reference/storage.md

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+# Storage — `client.storage` + `client.projectStorage`
+
+Two key/value stores: per-player (`StorageDomain`, revision key `storage`) and
+project-wide shared (`ProjectStorageDomain`, revision key `projectStorage`).
+Sources: `src/domains/StorageDomain.ts`, `src/domains/ProjectStorageDomain.ts`.
+
+## Player storage
+
+```ts
+client.storage.data    // GetStorageResponse | undefined
+await client.storage.save(items);
+await client.storage.delete(type);
+```
+
+```ts
+interface GetStorageResponse {
+  items?: StorageItem[];
+  nextCursor?: string;
+}
+interface StorageItem {
+  data?: string;   // opaque payload, JSON-stringify yourself if needed
+  id?: string;
+  type?: string;   // the storage "collection" key
+}
+```
+
+- `save(items: StorageItem[]): Promise<void>` — upserts items, then
+  invalidates the domain so subscribers refetch.
+- `delete(type: string): Promise<void>` — deletes **all** player storage items
+  of that type, then invalidates.
+
+## Project storage
+
+```ts
+client.projectStorage.data   // GetProjectStorageResponse | undefined
+await client.projectStorage.save(items);
+```
+
+```ts
+interface GetProjectStorageResponse {
+  items?: ProjectStorageItem[];
+  nextCursor?: string;
+}
+interface ProjectStorageItem {
+  data?: string;
+  expiresAt?: string;
+  id?: string;
+  readPermission?: 'public' | 'serverOnly';
+  size?: number;
+  type?: string;
+  updatedAt?: string;
+  version?: number;
+  writePermission?: 'public' | 'serverOnly';
+}
+interface ProjectStorageUpdateItem { data?: string; type?: string }
+```
+
+- `save(items: ProjectStorageUpdateItem[]): Promise<void>` — upserts, then
+  invalidates. Writing is only possible for items whose `writePermission` is
+  `public`; `serverOnly` items are read-only for clients.
+- The SDK exposes no client-side project-storage delete.
+
+## Limits and notes
+
+- Both domains load with `{ limit: 100 }` — the observable snapshot holds at
+  most 100 items and `nextCursor` pagination is not surfaced by the domain.
+- `data` is a raw string on the wire; serialize/deserialize JSON yourself.
+- Both are observable (`SyncedState`) and warmed by the revision poll only when
+  in use; mutations self-invalidate.