feat(skills): add shared task workflows

shared/skills/implementation/integration-test-write/SKILL.md

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+---
+name: integration-test-write
+description: Add focused integration tests for connected system behavior.
+---
+
+# Integration Test Write
+
+Identify the integration boundary, required setup, and meaningful success and failure cases.
+
+Keep the test deterministic and limited to the behavior under change.

shared/skills/implementation/sql-write/SKILL.md

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+---
+name: sql-write
+description: Implement a focused SQL change safely.
+---
+
+# SQL Write
+
+Understand the schema and affected data before writing SQL.
+
+Use the smallest complete change, preserve data safety, and run relevant verification.
+
+Do not execute destructive operations without explicit authorization.

shared/skills/implementation/unit-test-write/SKILL.md

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+---
+name: unit-test-write
+description: Add focused unit tests for isolated behavior.
+---
+
+# Unit Test Write
+
+Identify the behavior and important boundary cases, then add focused deterministic tests.
+
+Prefer observable behavior over implementation details. Report the checks that were run.