feat(skills): add shared task workflows

shared/skills/planning/change-impact-analysis/SKILL.md

@@ -0,0 +1,12 @@
+---
+name: change-impact-analysis
+description: Determine what a proposed change may affect.
+---
+
+# Change Impact Analysis
+
+Use when the blast radius or compatibility impact is uncertain.
+
+Inspect callers, dependencies, configuration, tests, and affected workflows.
+
+Return affected areas, risks, and recommended verification. Separate facts from assumptions.

shared/skills/planning/implementation-planner/SKILL.md

@@ -0,0 +1,12 @@
+---
+name: implementation-planner
+description: Create a concise plan for implementing an understood change.
+---
+
+# Implementation Planner
+
+Use before implementation when a change has multiple meaningful steps.
+
+Identify the goal, affected areas, sequence, risks, and verification.
+
+Return a short actionable plan. Do not implement the change.

shared/skills/planning/work-item-definition/SKILL.md

@@ -0,0 +1,12 @@
+---
+name: work-item-definition
+description: Turn an unclear request into a bounded technical work item.
+---
+
+# Work Item Definition
+
+Use when requirements, scope, or acceptance criteria are incomplete.
+
+Clarify the objective, boundaries, assumptions, acceptance criteria, and open questions.
+
+Do not invent business requirements.