Refactor task management structure and update documentation

- Changed the directory structure for task specifications to include a dedicated `todo/` folder within `_docs/02_tasks/` for tasks ready for implementation.
- Updated references in various skills and documentation to reflect the new task lifecycle, including changes in the `implementer` and `decompose` skills.
- Enhanced the README and flow documentation to clarify the new task organization and its implications for the implementation process.

These updates improve task management clarity and streamline the implementation workflow.

_docs/02_tasks/done/AZ-156_test_label_validation.md

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+# Label Validation Tests
+
+**Task**: AZ-156_test_label_validation
+**Name**: Label Validation Tests
+**Description**: Implement 5 blackbox tests for YOLO label validation — valid labels, out-of-range coords, missing files, multi-line corruption
+**Complexity**: 1 point
+**Dependencies**: AZ-152_test_infrastructure
+**Component**: Blackbox Tests
+**Jira**: AZ-156
+**Epic**: AZ-151
+
+## Problem
+
+Labels must be validated before dataset formation. Tests verify the check_label function correctly accepts valid labels and rejects corrupted ones.
+
+## Outcome
+
+- 5 passing pytest tests in `tests/test_label_validation.py`
+
+## Scope
+
+### Included
+- BT-LBL-01: Valid label accepted (returns True)
+- BT-LBL-02: Label with x > 1.0 rejected (returns False)
+- BT-LBL-03: Label with height > 1.0 rejected (returns False)
+- BT-LBL-04: Missing label file rejected (returns False)
+- BT-LBL-05: Multi-line label with one corrupted line (returns False)
+
+### Excluded
+- Integration with dataset formation (separate task)
+
+## Acceptance Criteria
+
+**AC-1: Valid label**
+Given label file with content `0 0.5 0.5 0.1 0.1`
+When check_label(path) is called
+Then returns True
+
+**AC-2: x out of range**
+Given label file with content `0 1.5 0.5 0.1 0.1`
+When check_label(path) is called
+Then returns False
+
+**AC-3: height out of range**
+Given label file with content `0 0.5 0.5 0.1 1.2`
+When check_label(path) is called
+Then returns False
+
+**AC-4: Missing file**
+Given non-existent file path
+When check_label(path) is called
+Then returns False
+
+**AC-5: Multi-line corruption**
+Given label with `0 0.5 0.5 0.1 0.1\n3 0.5 0.5 0.1 1.5`
+When check_label(path) is called
+Then returns False
+
+## Constraints
+
+- Label files are generated in tmp_path at test time
+- No external fixtures needed