Update JavaScript docs for v2 release

[simolus3]

Version 2 of the JavaScript SDK will:

• Replace js_logger with a custom interface and default console implementation.
• Refactor open and sync option types to avoid explicit factories in most cases.
• Encapsulate implementation details (doesn't require documentation changes).
• Moves uploading, downloading and errors from dataFlowStatus to the main SyncStatus interface.
• Simplify DBAdapter implementations (mostly internal, the website has no documentation on that interface).
• Load RSocket dynamically, and make HTTP the default on most SDKs.
• Merge web workers (relevant for React Native Web setup with custom copied workers).
• Remove CommonJS builds (doesn't require documentation changes).
• Remove RQNS support and make op-sqlite the only production database driver.
• Remove deprecated members (none of them are mentioned on the docs site).

This updates database instantiations and logger setups to reflect pending v2 changes.

AI use: I let Claude go through issues labelled tmp-js-v2 to generate an initial draft, which I've then checked and updated manually.

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