fix(react): serialize local storage seed initialization

[Egge21M]

Problem

localStorageSeedGetter() initialized a missing seed with a non-atomic localStorage read-generate-write sequence. Concurrent first-run tabs could each cache a different seed even though only the last seed written remained recoverable from storage.

Summary

• serialize seed initialization across same-origin browser contexts with an origin-scoped Web Lock
• fail before generating or writing when Web Locks are unavailable
• document the secure-context requirement and add a patch changeset
• add deterministic regression coverage for concurrent initializers and unsupported environments

Verification

• bun run --filter='@cashu/coco-react' test (50 tests passed)
• bun run --filter='@cashu/coco-react' typecheck
• bun run --filter='@cashu/coco-react' lint (passes with two existing warnings)
• bun run --filter='@cashu/coco-react' build
• bunx prettier --check packages/react/src/lib/utils/localStorageSeedGetter.ts packages/react/src/lib/utils/localStorageSeedGetter.test.ts packages/react/README.md .changeset/lock-local-storage-seeds.md

This issue was found by Project Loupe

[changeset-bot]

🦋 Changeset detected

Latest commit: d687d30

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 8 packages

Name	Type
@cashu/coco-react	Patch
@cashu/coco-core	Patch
@cashu/coco-indexeddb	Patch
@cashu/coco-expo-sqlite	Patch
@cashu/coco-sqlite	Patch
@cashu/coco-sqlite-bun	Patch
@cashu/coco-adapter-tests	Patch
@cashu/coco-sql-storage	Patch

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