Address the 11 October test report findings

The initial test report (run before the pilot-readiness changes) raised
seven findings and a retest plan. This closes the ones still open.

- F-01: a business on its free trial may run 2 active branches whatever
  its tier, so an owner can try transfers and per-branch stock. Only
  active branches count towards any limit.
- F-06: owners can rename branches and deactivate/reactivate them from
  the Branches page. A branch can only be deactivated once it holds no
  stock and no active staff; its history stays in every report, and it
  leaves every picker.
- F-04: the Products page lists deactivated products under a toggle with
  Reactivate. Deactivating warns about stock still on hand, which stays
  on the Stock page so it can be transferred or counted out.
- F-05: products carry a unit (L, ml, kg, g, pcs, tray, pack) instead of
  everything being litres.
- CAT-12: product prices must be above zero and names are unique per
  business, ignoring case.
- F-03: a reversed report period is refused by the page and the API, and
  the page labels which period the cards show. Report dates are Nairobi
  business days.
- F-07: cost of goods sold is units sold x average buying price. Stock
  bought in the period is reported separately, with a cash surplus line,
  so unsold stock no longer shows as a loss.
- STA-04: staff and new branch managers can be invited with a one-time,
  7-day link; the person sets their own password. Managers can issue a
  new link for their own cashiers.
- OFF-02 / POS-02: the till shows each product's stock and deducts every
  sale immediately, online or offline; it warns before selling more than
  the recorded stock, and has a Clear sale button.
- npm run backfill:stock turns purchases recorded before the stock ledger
  into stock, so existing tenants (and the report's ZERRO fixtures) start
  from what they bought.

tests/retest-plan.test.ts runs the report's completion and retest plan
and checks every balance and total it predicts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PILOT_READINESS.md

@@ -76,7 +76,7 @@ the decisions taken along the way, and what is still open.
   sales from the old version are sent on the next sync.
 
 ## Testing
-- `npm test` runs 37 API tests against an in-memory MongoDB, covering role
+- `npm test` runs 50 API tests against an in-memory MongoDB, covering role
   enforcement, tenant isolation for sales, stock and transfers, suspension,
   the sync protocol (including a 120-sale backlog replayed twice), and the
   business day.
@@ -84,9 +84,38 @@ the decisions taken along the way, and what is still open.
   in, stop the server, reload the terminal, record two sales, restart the
   server, confirm they sync once and deduct stock.
 
+## Follow-ups from the 11 October 2026 test report
+
+The initial test report (run on the build before these changes) raised
+seven findings and a retest plan. All of them are addressed on
+`fix/test-report-followups`:
+
+| Finding | What changed |
+|---|---|
+| F-01 Trial allows one branch | A business on its free trial may run **2 active branches** whatever its tier (`TRIAL_MAX_BRANCHES` in `src/lib/tiers.ts`). After the trial the tier's limit applies to adding branches. |
+| F-02 No current stock | Done in the previous change (stock ledger). Purchases recorded before the ledger existed are added by `npm run backfill:stock`. |
+| F-03 Reversed report dates | Refused in the page and by the API (400). The page labels which period the cards show. Report dates are Nairobi business days. |
+| F-04 No way back for deactivated products | Products page lists deactivated products under a toggle, with Reactivate. Deactivating warns about stock still on hand; that stock stays on the Stock page and can be transferred or counted out. |
+| F-05 Eggs shown as litres | Products carry a unit (L, ml, kg, g, pcs, tray, pack), chosen when the product is created and shown everywhere. |
+| F-06 No branch or staff removal | Staff: deactivate/reactivate (previous change). Branches: rename and deactivate/reactivate on the Branches page. A branch can only be deactivated once it has no stock and no active staff; its history stays in reports. |
+| F-07 Purchases shown as cost of goods | Cost of goods sold is now units sold x the product's average buying price. Purchases in the period are shown separately as "Stock purchased", with a "Cash surplus" line. |
+| STA-04 No invites | Staff and new branch managers can be invited: the owner or manager gets a one-time link (7 days) to send, and the person sets their own password. A new link can be made from Staff. |
+| CAT-12 Zero price, duplicates | Prices must be above zero; product names are unique per business, ignoring case. |
+| OFF-02 Local stock deduction | The till shows each product's stock and deducts every sale immediately, online or offline. |
+| POS-02 / INV-05 Oversell, cancel | The till warns before selling more than the recorded stock and asks to confirm (it does not block, because the sale may already have happened). A "Clear sale" button empties the cart. |
+
+`tests/retest-plan.test.ts` runs the report's completion and retest plan
+(online sale, transfer, two offline sales replayed twice, a Branch B sale)
+and checks every balance and total it predicts.
+
+### Before re-running the test report's plan on ZERRO
+1. Deploy, then run `npm run backfill:stock` once so the existing test
+   purchases count as stock. Run it **before** anyone records an opening
+   count, or those units would be counted twice.
+2. ZERRO is trialling, so it can now add Branch B without a plan change.
+3. Create the manager and cashier logins with invite links from Staff.
+
 ## Still open
-- **Removing a branch.** Branches can be renamed but not removed. Someone
-  needs to decide what happens to a removed branch's stock and history.
 - **Setting branch prices.** Branch price overrides are applied everywhere,
   but there is no screen or API to set them yet.
 - **Global email and phone uniqueness.** One person cannot work for two
@@ -96,9 +125,11 @@ the decisions taken along the way, and what is still open.
   route.
 - **Concurrent transfers.** Two transfers submitted at the same moment
   could together send more than the branch holds.
-- **Cash-basis profit.** The profit report counts all purchases in the
-  period as cost of goods.
+- **Cost of goods is an average.** It uses each product's average buying
+  price across the business, not first-in-first-out per branch. Units sold
+  with no purchase on record are counted and flagged, but have no cost.
 - **M-Pesa, if turned on.** Only one product per payment. A prompt that
   times out still needs a manual check before taking cash.
-- **Not modelled yet:** invites and email verification, empty-bottle and
-  deposit tracking, home-screen icons for the PWA.
+- **Not modelled yet:** email verification at signup, sending invites by
+  email (links are shared by hand, e.g. WhatsApp), empty-bottle and deposit
+  tracking, home-screen icons for the PWA.