refactor: remove duplicate AgentResponse/ChatResult dataclasses from core/types

refactor: convert PipelineResult from dataclass to Pydantic BaseModel

refactor: add ToolConfig pydantic model, replace tool_config dicts

refactor: extract derive_part_name, remove dead code from prompts.py

feat: add 3MF export and /api/models/{name}.3mf endpoint

refactor: eliminate all Serializer classes, use Pydantic model_dump() directly

refactor: typed Pydantic config + Pydantic result models, eliminate dict access

feat(cam): add CAMPlan Pydantic model for structured output

feat(cam): add generate_gcode function with ocp-freecad-cam wrapper

feat(cam): add CAMResult dataclass and serializer

refactor: config-drive all backends, use LLMBackend ABC from types

refactor: config-drive CNC validation thresholds

feat: add BackendFactory registry for centralized backend creation

feat: add serializers for execution and validation results

feat: add type system — enums, dataclasses, LLMBackend ABC

fix: address agentic review — security, prompts, retry, validation

refactor: reorganize codebase into core/, server/, agents/ packages