feat(release): self-determination - ensure at launch, drift warnings, M20 packages/* decision (#38)

- release.sh ensure: aligned no-op; drift -> package-if-needed + health-gated
  activate (M3 gate-then-flip, automated)
- ensure_release_aligned in common.sh: invoked by hello/verify/agent;
  MOSAIC_ENSURE_SKIP guards recursion; run-task warns on drift without
  auto-aligning (workers/suites never trigger builds or model gates)
- ROADMAP: M20 decision recorded - v2 adopts packages/* monorepo at usurpation
- BUILD-LOG Phase 20 + tool-race process note

Live-verified: post-reset pointer loss auto-restored via health-gated
ensure; drift warning fires on desired-version bump; idempotent no-op on
aligned state.

Closes #38

docs/plans/ROADMAP.md

@@ -120,10 +120,9 @@ usurpation, v2 content becomes THE next-branch content on
 mosaicstack/stack — a full refactor-and-replace with a functional system.
 Not ready yet.
 
-Open decision at usurpation time: whether v2 reorganizes to the stack
-monorepo layout (`packages/*` — continuity with existing tooling) or keeps
-its flat structure and defines the new convention (clean break). Reference
-for either: harvest worktree `~/src/mosaic-stack-worktrees/v2-harvest`
+DECIDED (owner, 2026-09-03): v2 reorganizes to the `packages/*` monorepo
+structure for continuity with the existing stack tooling and expectations.
+Reference: harvest worktree `~/src/mosaic-stack-worktrees/v2-harvest`
 (branch `next` @ 0db2d19a) and `packages/mosaic` (CLI), `packages/auth`.
 Usurpation criteria to be defined before any replacement (proposed:
 functional parity of P0 operations on the v2 runtime + owner sign-off).