Release 0.16.0

Added

• Config Bus: env_style (auto/nested/flat), max_depth, env_prefix auto-derivation, env_map (namespace + global), Config.env_map(), CONFIG_ENV_MAP_CONFLICT error.
• Context: ContextKey[T] typed accessor with get()/set()/delete()/exists()/scoped(). Built-in key constants (TRACING_SPANS, METRICS_STARTS, etc.). Context.serialize()/deserialize() with _context_version: 1.
• Annotations: extra: dict[str, Any] extension field on ModuleAnnotations. pagination_style changed from Literal to str. DEFAULT_ANNOTATIONS constant. from_dict() classmethod with unknown key capture.
• ACL: SyncACLConditionHandler / AsyncACLConditionHandler protocols. ACL.register_condition(). $or/$not compound operators. async_check() method. Fail-closed for unknown conditions.
• Pipeline: Step protocol, BaseStep ABC, StepResult, PipelineContext, PipelineTrace, ExecutionStrategy, PipelineEngine. 11 BuiltinStep classes. Preset strategies (standard/internal/testing/performance). Executor.strategy parameter. call_with_trace()/call_async_with_trace(). register_strategy()/list_strategies()/describe_pipeline().

Changed

• Middleware data keys migrated from legacy names (_metrics_starts etc.) to _apcore.mw.* convention using typed ContextKey.

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