feat(provider): implement the native Document driver (Percona Operator for MongoDB)

[devantler]

🤖 Generated by the Agentic Engineer

Child of #33. Blocked by the provider interface child — do not start before that contract exists.

User story

As a product author, I want type: document with provider: native to give me a production-grade MongoDB via the Percona Operator for MongoDB, so document workloads are not forced onto a Postgres emulation.

Acceptance criteria

• type: document + provider: native provisions through the Percona Operator and reports readiness from the operator's own documented conditions, surfacing actionable failures rather than a generic error.
• The connection contract is published as a Secret reference; no credentials enter the CR.
• The operator is a declared dependency with a pinned version, and its absence produces a clear, actionable condition rather than a crash or an indefinite pending state.
• Deletion policy and ownership are explicit and tested, including that deleting the DataProduct does not silently orphan or silently destroy data — whichever is chosen is documented.
• Both feature-flag states tested.

Open

Percona's operator is the named choice; if it is rejected on licensing or footprint grounds, record the alternative and why on #33 before implementing.

Rough size: L.