restore .ideai/tickets/ store versionnέ + corrige .gitignore

- Restaure .ideai/tickets/ depuis 851f1f8^ (167 tickets + index.json + counter.json)
- Enlève les ignore rules .ideai/tickets/ dans .gitignore (ligne 51 et 75)
- Permet le suivi durable du store tickets futur
- Ne touche pas sdk/ (reste untracked)

.ideai/tickets/51/issue.md

@@ -0,0 +1,15 @@
+---
+id: "6b74084c-0323-4f87-83f0-d9f944c364dc"
+number: 51
+title: "Clean des session headless"
+status: "open"
+priority: "medium"
+sprint: null
+links: []
+agentRefs: []
+createdBy: {"kind":"user"}
+updatedBy: {"kind":"user"}
+createdAt: 1783941336721
+updatedAt: 1783941336721
+version: 1
+---