fix: Preserve command namespace in Copilot skill names

Stop stripping namespace prefixes when converting commands to Copilot
skills. `workflows:plan` now becomes `workflows-plan` instead of just
`plan`, avoiding clashes with Copilot's own features in the chat UI.

Also updates slash command references in body text to match:
`/workflows:plan` → `/workflows-plan`.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/brainstorms/2026-02-17-copilot-skill-naming-brainstorm.md

@@ -0,0 +1,30 @@
+---
+date: 2026-02-17
+topic: copilot-skill-naming
+---
+
+# Copilot Skill Naming: Preserve Namespace
+
+## What We're Building
+
+Change the Copilot converter to preserve command namespaces when converting commands to skills. Currently `workflows:plan` flattens to `plan`, which is too generic and clashes with Copilot's own features in the chat suggestion UI.
+
+## Why This Approach
+
+The `flattenCommandName` function strips everything before the last colon, producing names like `plan`, `review`, `work` that are too generic for Copilot's skill discovery UI. Replacing colons with hyphens (`workflows:plan` -> `workflows-plan`) preserves context while staying within valid filename characters.
+
+## Key Decisions
+
+- **Replace colons with hyphens** instead of stripping the prefix: `workflows:plan` -> `workflows-plan`
+- **Copilot only** — other converters (Cursor, Droid, etc.) keep their current flattening behavior
+- **Content transformation too** — slash command references in body text also use hyphens: `/workflows:plan` -> `/workflows-plan`
+
+## Changes Required
+
+1. `src/converters/claude-to-copilot.ts` — change `flattenCommandName` to replace colons with hyphens
+2. `src/converters/claude-to-copilot.ts` — update `transformContentForCopilot` slash command rewriting
+3. `tests/copilot-converter.test.ts` — update affected tests
+
+## Next Steps
+
+-> Implement directly (small, well-scoped change)