Add shared docs mutation transport, reuse in CLI/HTTP, and extract maintenance helpers

[Intrinsical-AI]

Motivation

• Consolidate and harden transport-level validation for docs mutation payloads to avoid duplicated parsing logic across CLI and HTTP.
• Reduce duplication in HTTP schemas and CLI payload assembly to prevent semantic drift and make input contracts single-source-of-truth.
• Improve maintainability of multi-store delete logic by extracting preflight and vector-delete/rebuild steps into small helpers.

Description

• Add a new module core.services.docs_mutation_transport providing DocsMutationPayload, MutationUpsertPayload, validate_docs_mutation_payload, build_docs_mutation_intent, and build_docs_mutation_intent_from_raw using pydantic for shared transport validation and intent construction.
• Update the HTTP layer to reuse the shared builder via build_docs_mutation_intent and replace in-module schema duplication with DocsMutateRequest aliasing DocsMutationPayload and UpsertDocItem inheriting from MutationUpsertPayload.
• Update the CLI command to use build_docs_mutation_intent_from_raw and map pydantic ValidationError/ValueError into a ValueError for consistent error handling.
• Extract maintenance helpers _preflight_vector_store_or_resolve_embedder and _delete_vector_rows_or_rebuild and wire them into delete_documents_multi_store and delete_external_ids_multi_store to centralize preflight checks and rebuild-on-failure logic while preserving behavior.
• Add unit tests tests/unit/core/services/test_docs_mutation_transport.py covering normalization, validation, conflict detection, and intent building.

Testing

• Ran the targeted test set with uv run pytest -q -o addopts='' tests/unit/core/use_cases/test_docs_mutation_refactor.py tests/unit/core/services/test_maintenance.py tests/unit/core/services/test_evaluation.py tests/unit/application/services/test_mutation_ports.py tests/unit/cli/test_cli_mutation_boundary.py tests/unit/http/test_docs_index_ports_wiring.py and observed 50 tests passed.
• Added tests/unit/core/services/test_docs_mutation_transport.py which exercises the new transport validation and intent builder and passed as part of the run.
• No automated test failures were introduced by these changes.

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Codex Task