fix: gate skills by OS

skills/imsg/SKILL.md

@@ -2,7 +2,7 @@
 name: imsg
 description: iMessage/SMS CLI for listing chats, history, watch, and sending.
 homepage: https://imsg.to
-metadata: {"clawdis":{"emoji":"📨","requires":{"bins":["imsg"]},"install":[{"id":"brew","kind":"brew","formula":"steipete/tap/imsg","bins":["imsg"],"label":"Install imsg (brew)"}]}}
+metadata: {"clawdis":{"emoji":"📨","os":["darwin"],"requires":{"bins":["imsg"]},"install":[{"id":"brew","kind":"brew","formula":"steipete/tap/imsg","bins":["imsg"],"label":"Install imsg (brew)"}]}}
 ---
 
 # imsg

skills/peekaboo/SKILL.md

@@ -2,7 +2,7 @@
 name: peekaboo
 description: Capture and automate macOS UI with the Peekaboo CLI.
 homepage: https://peekaboo.boo
-metadata: {"clawdis":{"emoji":"👀","requires":{"bins":["peekaboo"]},"install":[{"id":"brew","kind":"brew","formula":"steipete/tap/peekaboo","bins":["peekaboo"],"label":"Install Peekaboo (brew)"}]}}
+metadata: {"clawdis":{"emoji":"👀","os":["darwin"],"requires":{"bins":["peekaboo"]},"install":[{"id":"brew","kind":"brew","formula":"steipete/tap/peekaboo","bins":["peekaboo"],"label":"Install Peekaboo (brew)"}]}}
 ---
 
 # Peekaboo

skills/things-mac/SKILL.md

@@ -2,7 +2,7 @@
 name: things-mac
 description: Manage Things 3 via the `things` CLI on macOS (add/update projects+todos via URL scheme; read/search/list from the local Things database). Use when a user asks Clawdis to add a task to Things, list inbox/today/upcoming, search tasks, or inspect projects/areas/tags.
 homepage: https://github.com/ossianhempel/things3-cli
-metadata: {"clawdis":{"emoji":"✅","requires":{"bins":["things"]},"install":[{"id":"go","kind":"go","module":"github.com/ossianhempel/things3-cli/cmd/things@latest","bins":["things"],"label":"Install things3-cli (go)"}]}}
+metadata: {"clawdis":{"emoji":"✅","os":["darwin"],"requires":{"bins":["things"]},"install":[{"id":"go","kind":"go","module":"github.com/ossianhempel/things3-cli/cmd/things@latest","bins":["things"],"label":"Install things3-cli (go)"}]}}
 ---
 
 # Things 3 CLI