Enhance .cursor documentation and workflows

Updated the README.md to reflect new skill commands and improved descriptions for various workflows, including the addition of new skills like /test-spec, /code-review, and /release. Enhanced clarity on session boundaries and flow resolutions in the auto-chaining process.

Removed the implementer agent file as it is no longer needed. Updated coderule and meta-rule documents to enforce stricter testing and implementation standards, ensuring real results are produced rather than simulated ones.

Revised the autodev flow documentation to include a new release step and clarified the retrospective process. Adjusted the testing rules to specify coverage thresholds for critical paths.

Co-authored-by: Cursor <cursoragent@cursor.com>

.cursor/skills/test-spec/phases/03-data-validation-gate.md

@@ -1,7 +1,7 @@
 # Phase 3: Test Data & Expected Results Validation Gate (HARD GATE)
 
 **Role**: Professional Quality Assurance Engineer
-**Goal**: Ensure every test scenario produced in Phase 2 has concrete, sufficient test data. Remove tests that lack data. Verify final coverage stays above 75%.
+**Goal**: Ensure every test scenario produced in Phase 2 has concrete, sufficient test data. Remove tests that lack data. Verify final coverage stays above the canonical threshold (currently 75% — see `.cursor/rules/cursor-meta.mdc` Quality Thresholds; never hardcode a different number in any phase).
 **Constraints**: This phase is MANDATORY and cannot be skipped.
 
 ## Step 1 — Build the requirements checklist