feat(PBI-76): migrate cookie-based prefs to user-settings (Phase 2) (#189)

* feat(PBI-76): extend UserSettings schema with layout

Adds layout.splitPanePositions and layout.activeSprints. These will
hold values currently kept in client-side and server-side cookies
(Phase 2). Two new tests cover the shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-76): migrate SplitPane positions to user-settings store

Outside of a drag the store is the source of truth (cross-tab
updates flow in for free). During a drag we keep splits in local
state so mousemove does not round-trip through the store. On
mouseup we persist the final splits via setPref. Removes
document.cookie reads/writes — cookieKey is reused as the
store-key for backwards compat.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-76): resolveActiveSprint reads from User.settings

lib/active-sprint:
- New helpers: getActiveSprintIdFromSettings, setActiveSprintInSettings,
  clearActiveSprintInSettings — all read/write user.settings.layout.activeSprints.
- resolveActiveSprint(productId, userId) — userId now required, falls back
  to first OPEN, then most recent CLOSED sprint.
- Cookie helpers (getActiveSprintIdFromCookie/setActiveSprintCookie/
  clearActiveSprintCookie) removed.

Callers updated to pass session.userId. The cookie-based fallback path
is gone — `actions/active-sprint.ts` and `actions/sprints.ts` will be
updated in the next commit (T-917).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-76): rewrite setActiveSprint callers to use settings

setActiveSprintAction, syncActiveSprintCookieAction, and the two
sprint-creation paths in actions/sprints.ts now write through
setActiveSprintInSettings (which also emits pg_notify for cross-tab
sync) instead of dropping a cookie. The action names keep the
'cookie' suffix in the user-visible API for now — clean rename can
come later.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-76): migration helper v2 — handle legacy cookies

Bumps marker version to 'v2'. buildMigrationPatch now also scans
document.cookie for `sp:*` (split-pane positions) and
`active_sprint_*` (active sprint per product) and lifts them into
layout.splitPanePositions / layout.activeSprints. clearLegacyStorage
replaces clearLegacyLocalStorage and clears both keys and cookies.
clearLegacyLocalStorage stays as a deprecated alias so the bridge
upgrade is a single rename.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* test(PBI-76): align tests with new SplitPane and active-sprint flow

- split-pane.test.tsx: seed positions via Zustand store instead of
  document.cookie; mock @/actions/user-settings so the prisma client
  is not transitively initialised in jsdom.
- backlog-split-pane.test.tsx: same action mock.
- sprint-dates.test.ts: add user.findUnique/update + $executeRaw
  mocks because createSprintAction now writes to user-settings.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/(app)/layout.tsx

@@ -47,7 +47,7 @@ export default async function AppLayout({ children }: { children: React.ReactNod
     })
     if (product) {
       activeProduct = product
-      const resolved = await resolveActiveSprint(product.id)
+      const resolved = await resolveActiveSprint(product.id, session.userId)
       hasActiveSprint = !!resolved
     } else {
       await prisma.user.update({

app/(app)/products/[id]/page.tsx

@@ -38,7 +38,7 @@ export default async function ProductBacklogPage({ params, searchParams }: Props
 
   const [user, switcherData] = await Promise.all([
     prisma.user.findUnique({ where: { id: session.userId! }, select: { active_product_id: true } }),
-    getSprintSwitcherData(id),
+    getSprintSwitcherData(id, { userId: session.userId }),
   ])
   const { sprintItems, buildingSprintIds, activeSprintItem } = switcherData
   const hasOpenSprint = sprintItems.some(s => s.status === 'open')

app/(app)/products/[id]/sprint/page.tsx

@@ -1,4 +1,5 @@
 import { redirect } from 'next/navigation'
+import { requireSession } from '@/lib/auth-guard'
 import { resolveActiveSprint } from '@/lib/active-sprint'
 
 interface Props {
@@ -7,7 +8,8 @@ interface Props {
 
 export default async function SprintRedirectPage({ params }: Props) {
   const { id } = await params
-  const active = await resolveActiveSprint(id)
+  const session = await requireSession()
+  const active = await resolveActiveSprint(id, session.userId)
   if (!active) {
     redirect(`/products/${id}?alert=no_sprint`)
   }