Keep the sidebar watch plan out of the initial bundle after rebasing

The watch plan and unwatched-project rotation are used only by the lazily
loaded sidebar count module, but they lived in document-actions.tsx, which
pulled sidebar-decision-watch into the initial chunk. Moving them to
sidebar-decision-plan.ts brings the merged build back within main's
unchanged budget. This also renews the navigation-shell and project-sidebar
design-contract hashes after the rebase (their reviewed dynamic class
expressions are unchanged), and widens the touch sidebar test to 1280px
because main now shows the inline sidebar only from 1198px.

Refs #345

Assistant-model: Claude Opus 5.5 (fast)
Assistant-workflow: inline
Assistant-verification: bun run build passed: initial JavaScript 255399 B raw / 80505 B gzip within 256000 / 81500 (main alone builds 251596 / 79505)
Assistant-verification: bun test passed: 4404 pass, 3 skip, 0 fail with commit.gpgsign=false for the command only
Assistant-verification: postgres contract tests passed: 76/76 against a disposable postgres:17 with migration 017
Assistant-verification: Playwright E2E passed: sidebar-decision-counts 12/12 after the viewport fix
Assistant-verification: bun run types and bun run ci passed: design contract ok, no new Impeccable findings
Co-authored-by: Alex Lavaee <lavaman131@github.com>