release(v4.3.0): browser persistence via @shade/storage-indexeddb

Ship an official IndexedDB-backed StorageProvider so browser-based Shade
consumers persist identity, prekeys, sessions, retired identities,
peer-verification state and stream-resume rows across tab refresh and
browser restart. Closes the gap that forced browser apps onto
storage:"memory" (regenerated identity each load, orphaned device
records server-side).

- New package @shade/storage-indexeddb (4.3.0): full StorageProvider
  conformance, schema v1, idb-backed; bumpPeerIdentityVersion is wrapped
  in a single readwrite IDB transaction (atomic, vs SQLite's
  read-then-upsert race).
- @shade/sdk resolveStorage() accepts { type: 'indexeddb', dbName? } via
  dynamic import (lazy, optional dep — same pattern as
  @shade/storage-postgres). Named StorageSpec type now reused by
  ResolvedConfig.
- Tests: 16 new tests in shade-storage-indexeddb (StorageProvider
  surface + peer-verifications + full E2EE conversation surviving a
  simulated tab reload). Run on fake-indexeddb.
- Lockstep version bump 4.2.1 → 4.3.0 across all 25 packages.
- Publish scripts updated to include the new package.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shade-sdk/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@shade/sdk",
-  "version": "4.2.1",
+  "version": "4.3.0",
   "type": "module",
   "main": "src/index.ts",
   "types": "src/index.ts",