Add Stock catalog (items/warehouses) and fix session persistence

Stock is scoped to a catalog + cost centers only, per direction that
physical GRV/stock-take/recipe transactions belong in an external
system (Matrix), not this accounting app. Stock Control/GRN/Variance/
PPV GL accounts are now plain postable accounts rather than locked
control accounts.

Also fixes session loss on page refresh: auth stores now persist to
localStorage, and ProtectedRoute waits for rehydration before deciding
to redirect to login.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JWqiUSojMLUoN7mrJqdEbN

PHASE_4_STOCK_TEST_PLAN.md

@@ -0,0 +1,44 @@
+# Phase 4 — Stock Simplification + Session Persistence: Manual Test Checklist
+
+This replaces the earlier version of this checklist. On review, the full transactional Stock
+module (GRV, Stock Takes, Recipe production) was removed — this is accounting software, not a
+stock/warehouse system, and those physical stock transactions belong in an external system
+(Matrix) instead. What remains: a Stock Item catalog, Warehouses as cost centers, and a
+Stock-on-Hand view that a future external feed will populate (currently empty — nothing in this
+app writes to it). This checklist also covers the session-persistence fix.
+
+## 1. Session persistence (the "logged out on refresh" fix)
+
+- [ ] Sign in through the Manager, land in the company app
+- [ ] Refresh the browser tab (F5) — you should **stay logged in**, not bounce back to the
+      Manager
+- [ ] Close the browser tab entirely and reopen `http://localhost:5173` — you should still be
+      signed in
+- [ ] Sign out — refreshing afterward should correctly show you signed out (not silently
+      restore the old session)
+- [ ] Same checks on the Manager itself (`http://localhost:5174`): refresh keeps you logged in,
+      sign out actually signs out
+
+## 2. Simplified Stock module
+
+- [ ] Sidebar's **Stock** section now shows only **Stock Items** (Recipes, Goods Received,
+      Stock Takes are gone)
+- [ ] Administration still has **Warehouses**
+- [ ] "New Stock Item" only asks for code, name, and unit of measure — no costing method
+- [ ] "New Warehouse" is unchanged (code, name, branch)
+- [ ] Stock Items page still has an "Items" tab and a "Stock Levels" tab; the Stock Levels tab
+      shows a note that quantities come from an external system, and the grid is empty (that's
+      expected — nothing populates it yet)
+- [ ] No "Match to GRV" button appears anywhere on a supplier's page
+- [ ] AP invoice lines only ever offer a plain expense account — no GRV-matching option
+- [ ] `GET /api/stock/grv`, `/api/stock/adjustments`, `/api/stock/recipes` all now 404 (removed)
+
+## 3. Regression: everything else unaffected
+
+- [ ] GL, AR, and AP all work exactly as before — Stock Control, Stock Variance, and the
+      account previously called "Goods Received Not Invoiced" / "Purchase Price Variance" are
+      now plain, normal GL accounts (no longer locked as control accounts), so they can be
+      posted to like any other account via a manual journal entry if you want to record a
+      stock-value adjustment by hand
+- [ ] The manual-journal control-account lockout still correctly blocks direct postings to AR
+      Control, AP Control, Tax accounts, and Bank accounts