Implement Rocks factory, capability negotiation, recovery, and generation lifecycle

[kylebernhardy]

Outcome

Make Rocks mode safely usable by standalone rocksdb-js applications and Harper through the same implementation.

Acceptance criteria

• The factory accepts only a versioned rocksdb-js native lease and never opens RocksDB itself.
• ABI major compatibility and additive capabilities are negotiated before opening an index.
• Lease identity prevents use after close, drop, or column-family recreation.
• Startup seals or removes abandoned working objects according to the last visible binding and never publishes unsealed objects.
• Orphan reclamation and active/shadow generation deletion are bounded and crash-safe.
• Close, backup, checkpoint, drop, and database background-error/write-stall behavior are deterministic.
• Harper hooks wrap the standalone factory rather than fork its storage code.

Comment generated by kAIle (Codex GPT-5)