[kafka] Implement Metadata API for pre-created Fluss tables

### Parent issue

Part of #4185 — Kafka Protocols Compatibility: Basic Produce.

### Motivation

Standard Kafka producers need metadata discovery before they can send records. Expose tables created through Fluss DDL as Kafka topics while preserving the DDL-defined table and schema lifecycle.

### Scope

- Implement Kafka Metadata v0-v11 over a narrow metadata backend and the TabletServer gateway.
- Reuse the table/topic mapping and schema validation contract from #4275; return brokers, partitions, leaders, replica assignments, ISR, and offline replicas for compatible tables.
- Preserve the Kafka listener context when resolving advertised endpoints.
- Handle invalid or missing topics, unavailable leaders, gateway failures, and table-deletion races.
- Respect authoritative ISR when bucket metadata provides it, with a conservative available-leader fallback for legacy metadata.
- Register Metadata so ApiVersions advertises the implemented capability.

### Acceptance criteria

- [ ] Named-topic, all-topic, and empty-topic discovery follow the DDL mapping contract and return the expected broker and partition metadata.
- [ ] Unsupported table mappings do not affect valid topics in the same request.
- [ ] Version boundaries and invalid requests, including missing names in v10/v11, are handled correctly.
- [ ] Replica/ISR reporting, legacy fallback, and error paths have regression coverage.
- [ ] Relevant handler, mapping, transport, and integration tests and style checks pass.
- [ ] The focused implementation is reviewed and merged after its prerequisites.

### Dependencies

PR04 in the foundation sequence. Depends on the PR03 DDL table mapping contract (#4275), which builds on #4265 and #4264.

### Out of scope

Kafka CreateTopics/DeleteTopics, automatic table creation, Metadata v12+ or ID-only topic lookup, Produce, authentication, and JSON-to-row conversion. Schema-aware JSON Produce is a later issue under #4185; this stage only provides discovery for pre-created tables.

### Implementation and review

Implementation PR: #4261.

The PR remains a draft while its prerequisites are pending. Its description includes an incremental comparison for reviewing Metadata alone.

Start by reading implementation PR #4261 and its incremental comparison, then review the PR03 DDL table mapping contract in #4275 and the prerequisites #4265 and #4264. Trace the handler, mapping, transport, and integration tests mentioned in the issue; done means the Metadata v0-v11 acceptance criteria and relevant regression and style checks pass.

Written by the indexing model from the issue text.