feat(tasks): teach agents when to use the task tools

The task tools were registered but had only mechanical descriptions and no
standing policy, so agents knew the tools existed but not when to reach for
them. Lead each of the five descriptions with its trigger (when to use, when
not to) and add a task-tracking convention to .correx/project.toml, which is
rendered into every stage's L0 context.

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

.correx/project.toml

@@ -5,6 +5,7 @@ conventions = [
     "Dependency direction: apps -> core -> infrastructure; no cross-core imports",
     "No bare try-catch; use runCatching and sealed domain error types",
     "Every new EventPayload must be registered in the eventModule polymorphic block (Serialization.kt)",
+    "Track multi-session or handoff work as native tasks: search before creating to avoid duplicates (task_search), task_context before starting, claim before working, submit_for_review when ready, complete after review. Don't open a task for a single self-contained edit you finish now.",
 ]
 
 [commands]