Refactor constants management to use Pydantic BaseModel for configuration

- Replaced module-level path variables in constants.py with a structured Pydantic Config class.
- Updated all relevant modules (train.py, augmentation.py, exports.py, dataset-visualiser.py, manual_run.py) to access paths through the new config structure.
- Fixed bugs related to image processing and model saving.
- Enhanced test infrastructure to accommodate the new configuration approach.

This refactor improves code maintainability and clarity by centralizing configuration management.

_docs/02_document/modules/annotation_queue_dto.md

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+# Module: annotation-queue/annotation_queue_dto
+
+## Purpose
+Data transfer objects for the annotation queue consumer. Defines message types for annotation CRUD events received from a RabbitMQ Streams queue.
+
+## Public Interface
+
+### AnnotationClass (local copy)
+Same as dto/annotationClass but reads `classes.json` from current working directory and adds `opencv_color` BGR field.
+
+### AnnotationStatus (Enum)
+| Member | Value |
+|--------|-------|
+| Created | 10 |
+| Edited | 20 |
+| Validated | 30 |
+| Deleted | 40 |
+
+### SourceEnum (Enum)
+| Member | Value |
+|--------|-------|
+| AI | 0 |
+| Manual | 1 |
+
+### RoleEnum (Enum)
+| Member | Value | Description |
+|--------|-------|-------------|
+| Operator | 10 | Regular annotator |
+| Validator | 20 | Annotation validator |
+| CompanionPC | 30 | Companion device |
+| Admin | 40 | Administrator |
+| ApiAdmin | 1000 | API-level admin |
+
+`RoleEnum.is_validator() -> bool`: Returns True for Validator, Admin, ApiAdmin.
+
+### Detection
+| Field | Type |
+|-------|------|
+| `annotation_name` | str |
+| `cls` | int |
+| `x`, `y`, `w`, `h` | float |
+| `confidence` | float (optional) |
+
+### AnnotationCreatedMessageNarrow
+Lightweight message with only `name` and `createdEmail` (from msgpack fields 1, 2).
+
+### AnnotationMessage
+Full annotation message deserialized from msgpack:
+| Field | Type | Source |
+|-------|------|--------|
+| `createdDate` | datetime | msgpack field 0 (Timestamp) |
+| `name` | str | field 1 |
+| `originalMediaName` | str | field 2 |
+| `time` | timedelta | field 3 (microseconds/10) |
+| `imageExtension` | str | field 4 |
+| `detections` | list[Detection] | field 5 (JSON string) |
+| `image` | bytes | field 6 |
+| `createdRole` | RoleEnum | field 7 |
+| `createdEmail` | str | field 8 |
+| `source` | SourceEnum | field 9 |
+| `status` | AnnotationStatus | field 10 |
+
+### AnnotationBulkMessage
+Bulk operation message for validate/delete:
+| Field | Type | Source |
+|-------|------|--------|
+| `annotation_names` | list[str] | msgpack field 0 |
+| `annotation_status` | AnnotationStatus | field 1 |
+| `createdEmail` | str | field 2 |
+| `createdDate` | datetime | field 3 (Timestamp) |
+
+## Internal Logic
+- All messages are deserialized from msgpack binary using positional integer keys.
+- Detections within AnnotationMessage are stored as a JSON string inside the msgpack payload.
+- Module-level `annotation_classes = AnnotationClass.read_json()` is loaded at import time for Detection.__str__ formatting.
+
+## Dependencies
+- `msgpack` (external) — binary message deserialization
+- `json`, `datetime`, `enum` (stdlib)
+
+## Consumers
+annotation-queue/annotation_queue_handler
+
+## Data Models
+AnnotationClass, AnnotationStatus, SourceEnum, RoleEnum, Detection, AnnotationCreatedMessageNarrow, AnnotationMessage, AnnotationBulkMessage.
+
+## Configuration
+Reads `classes.json` from current working directory.
+
+## External Integrations
+None (pure data classes).
+
+## Security
+None.
+
+## Tests
+None.