feat(sandbox): Landlock no-op sous Posture::Allow (allow-by-default)

Un allowlist Landlock ne peut que retirer des accès (deny-by-default). Sous
une fallback Posture::Allow (allow-by-default), enforcer les grants
verrouillerait tout hors du project root — binaire CLI, libs et ~/.<cli> —
provoquant le 'failed to open terminal'. On n'enforce donc rien sous Allow ;
seuls les Deny explicites font foi (advisory via la projection LP3).
Couvre permissions.json persisté avec fallback allow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.ideai/permissions.json

@@ -0,0 +1,38 @@
+{
+  "version": 1,
+  "projectDefaults": {
+    "rules": [
+      {
+        "capability": "read",
+        "effect": "allow",
+        "paths": [
+          "**"
+        ],
+        "commands": []
+      },
+      {
+        "capability": "write",
+        "effect": "allow",
+        "paths": [
+          "**"
+        ],
+        "commands": []
+      },
+      {
+        "capability": "delete",
+        "effect": "allow",
+        "paths": [
+          "**"
+        ],
+        "commands": []
+      },
+      {
+        "capability": "executeBash",
+        "effect": "allow",
+        "paths": [],
+        "commands": []
+      }
+    ],
+    "fallback": "allow"
+  }
+}