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-158_test_model_split.md

@@ -0,0 +1,44 @@
+# Model Split Tests
+
+**Task**: AZ-158_test_model_split
+**Name**: Model Split Tests
+**Description**: Implement 2 blackbox tests for model split storage — size constraint and reassembly integrity
+**Complexity**: 1 point
+**Dependencies**: AZ-152_test_infrastructure
+**Component**: Blackbox Tests
+**Jira**: AZ-158
+**Epic**: AZ-151
+
+## Problem
+
+Encrypted models are split into small and big parts for CDN storage. Tests must verify the split respects size constraints and reassembly produces the original.
+
+## Outcome
+
+- 2 passing pytest tests in `tests/test_model_split.py`
+
+## Scope
+
+### Included
+- BT-SPL-01: Split respects size constraint (small ≤ max(3072 bytes, 20% of total))
+- BT-SPL-02: Reassembly produces original (small + big == encrypted bytes)
+
+### Excluded
+- CDN upload/download (requires external service)
+
+## Acceptance Criteria
+
+**AC-1: Size constraint**
+Given 10000 encrypted bytes
+When split into small + big
+Then small ≤ max(3072, total × 0.2); big = remainder
+
+**AC-2: Reassembly**
+Given split parts from 10000 encrypted bytes
+When small + big concatenated
+Then equals original encrypted bytes
+
+## Constraints
+
+- Uses generated binary data (no fixture files needed)
+- References SMALL_SIZE_KB constant from constants.py