Add entities namespace and activate memory pipeline hooks

[ethanj]

Summary

Adds the entities namespace (EntitiesClient / AsyncEntitiesClient) over /v1/entities, activates memory pipeline hooks that were previously accepted at registration but never invoked, and introduces two narrower error subclasses for TS SDK parity.

Changes

Entities namespace

• Add atomicmemory/entities/ package: types.py (Pydantic wire models), client.py (sync), async_client.py (async), errors.py (EntitiesClientError).
• Wire client.entities onto AtomicMemoryClient and AsyncAtomicMemoryClient using the same transport config, closed with the client.
• Export all entity types and both client classes from the package root.
• Operations: profile, list, get, delete, attributes, memory_history, patch_settings, merge.
• Python field names match the snake_case wire 1:1 — no camelCase mapping layer.

Memory pipeline hooks

• MemoryService and AsyncMemoryService now execute registered pipeline hooks: preprocess_ingest (may split one input into many; per-item results merge in order), postprocess_ingest, preprocess_search, postprocess_search, preprocess_get, postprocess_get, and postprocess_list.
• delete and package take no pipeline hooks, matching TS semantics.
• Add AsyncMemoryProcessingPipeline and NOOP_ASYNC_PIPELINE; export from atomicmemory.memory.
• MemoryProcessingPipeline hook signatures are now synchronous; the async surface uses AsyncMemoryProcessingPipeline.

Error subclasses

• Add UnsupportedOperationError (subclass of ProviderError) and InvalidScopeError (subclass of ValidationError); existing except ProviderError / except ValidationError handlers keep working.
• Export both from the package root.

API key handling

• api_key fields in AtomicMemoryClientConfig and EntitiesClientConfig changed to SecretStr to prevent accidental logging. The secret value is extracted only at the transport call site.

Client close semantics

• AtomicMemoryClient.close() aligned with AsyncAtomicMemoryClient.close(): first-error-wins across all three namespaces; previously a later namespace's failure silently replaced an earlier one.

CI

• Add .github/workflows/publish-pypi.yml: manual, version-gated OIDC Trusted Publishing workflow; guarded to run only on the public repository.

Why

• The entities namespace is required for agent workflows that read entity profiles, inspect attribute triples, and merge duplicate entities — previously only accessible via raw HTTP.
• Pipeline hooks have been part of the registration API since the initial release but had no effect; callers supplying hooks for content splitting or result logging received no errors and no execution.
• UnsupportedOperationError and InvalidScopeError allow callers to catch specific failure modes without parsing error messages, matching the TS SDK's discriminated error hierarchy.
• SecretStr ensures API keys are redacted in Pydantic repr and default logging paths without changing the external dict-based config interface.

Validation

• tests/entities/ — 7 new test modules covering sync/async client round-trips, input validation, response validation, and type models (~1,280 lines).
• tests/test_pipeline_hooks.py / tests/test_pipeline_hooks_async.py — hook invocation order, split-ingest merging, postprocess receives processed request (~460 lines).
• tests/test_error_subclasses.py — subclass hierarchy, isinstance compatibility with parent handlers (~256 lines).
• tests/test_api_key_redaction.py — SecretStr repr, no plaintext key in error messages (~149 lines).
• tests/_pipeline_fakes.py — shared fake pipeline/provider infrastructure extracted from client tests.