feat(tasks): task_decompose splits a goal into a dependency-linked graph in one approval

The freestyle analyst can now break a large goal with dependency seams or
independent review/handoff points into a parent epic + DEPENDS_ON-linked children
in a single T2 approval, instead of N separate task_create calls. Parent
DEPENDS_ON every child (completes last); each child IMPLEMENTS parent. Resolves
depends_on by ref or index; rejects cycles, unresolved refs, missing title/goal,
and empty batches; same batch dedup + force_reason convention as task_create.

A session works one active task, so multi-task work is multi-session by
construction: the analyst names the single ready task this run works, the architect
threads only that one, and siblings are claimed by later runs via task_ready
(claim-driven; no scheduler, /tasks/next stays rejected).

Doctrine: analyst_freestyle.md picks one-task-vs-decompose and names the ready
task; architect_freestyle.md threads only that one; plus the L0 policy line.
freestyle_planning.toml analyst gains task_decompose (pinned by
FreestylePlanningWorkflowTest).

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

.correx/project.toml

@@ -5,7 +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.",
+    "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. When a goal has dependency seams or independent review points, task_decompose it into a parent + DEPENDS_ON-linked children (one approval) instead of one big task; a session works one task at a time, so siblings are claimed by later runs as they unblock.",
 ]
 
 [commands]