feat(filesystem): add makeOpfsFileSystem OPFS storage adapter

[deny-dz]

Summary

This PR introduces makeOpfsFileSystem to @solid-primitives/filesystem:

• Origin Private File System (OPFS) Support: Implements the FSAdapter interface over navigator.storage.getDirectory().
• Zero Permission Prompts: Unlike showDirectoryPicker(), OPFS does not trigger user confirmation dialogs on access, making it the ideal browser storage layer for local-first databases (SQLite WASM, PGLite), offline asset caching, audio stems, and document vaults.
• Full CRUD Support: Supports getType, readdir, mkdir, readFile, writeFile, and rm with nested path resolution.

Changes

• packages/filesystem/src/adapter-opfs.ts: Core OPFS adapter implementation.
• packages/filesystem/src/index.ts: Re-export makeOpfsFileSystem.
• packages/filesystem/test/opfs.test.ts: Vitest test suite.
• .changeset/filesystem-opfs-adapter.md: Minor changeset.

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🦋 Changeset detected

Latest commit: 80351cf

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

This PR includes changesets to release 1 package

Name	Type
@solid-primitives/filesystem	Minor

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Reviewing files that changed from the base of the PR and between c7b608c and 80351cf.

📒 Files selected for processing (4)

• .changeset/filesystem-opfs-adapter.md
• packages/filesystem/src/adapter-opfs.ts
• packages/filesystem/src/index.ts
• packages/filesystem/test/opfs.test.ts

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