Disable Kafka connector and gRPC, restrict backend to REST, add hygiene checks and tests

[neuron7xLab]

Motivation

• Make unsupported ingestion surfaces explicit by removing Kafka/gRPC as supported runtime paths and ensure connectors fail closed rather than silently stubbing behavior.
• Prevent placeholder/TBD tokens from leaking into generated stakeholder artifacts.
• Add focused connector hygiene tests and wire them into the PR gate so connector regressions are caught automatically.

Description

• Reworked Kafka handling by turning the old stub into a fail-closed implementation that raises KafkaConnectorUnavailableError in src/.../connectors/kafka_source.py and exported the explicit error.
• Removed KafkaSourceConfig and Kafka options from src/.../connectors/config.py, restricted BackendConfig.protocol and IngestionConfig.source_type to supported values (rest/file), and added validation to reject unsupported protocols.
• Simplified and hardened RemoteBackend in src/.../connectors/runner.py to be REST-only, added a protocol check that raises on non-REST protocols, and consolidated HTTP client usage.
• Added placeholder detection to scripts/generate_stakeholder_assets.py via PLACEHOLDER_RE and assert_no_placeholders, and cleaned up a couple of TBD entries.
• Added new tests: tests/connectors/test_fail_closed_connectors.py, tests/connectors/test_polygon_adapter_reproducible.py, and scripts/tests/test_generate_stakeholder_assets.py, and removed the legacy tests/unit/data/adapters/test_polygon.py.
• Updated CI (.github/workflows/pr-gate.yml) to run the new mandatory connector hygiene tests as part of the PR gate.

Testing

• Ran the fast unit test suite with pytest tests/ -q and the run completed successfully.
• Executed the new connector hygiene tests with pytest tests/connectors/test_fail_closed_connectors.py tests/connectors/test_polygon_adapter_reproducible.py scripts/tests/test_generate_stakeholder_assets.py -q and they passed.
• CI workflow updated to run the new connector hygiene tests as part of the PR gate and the added tests are included in that job.

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Codex Task

[chatgpt-codex-connector]

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