v12.0.0 — Register correctness pass, and the till is a PWA only

v12.0.0 — Register correctness pass, and the till is a PWA only

A full review of src/pos/ turned up sixteen defects, from a receipt printed with no
number on it to a real sale that could sit invisible in the outbox forever. All of them
are fixed here. Separately, the Tauri desktop shell is gone: the register ships as a PWA
and only as a PWA.

Consumer action required on upgrade

commitPosSale now returns the priced lines it already computes, and the register builds
the customer's receipt from those. Redeploy the caspian-pos codebase or receipts keep
falling back to the till's scanned prices:

npm install github:CaspianTools/script-caspian-store#v12.0.0
cd firebase/functions-pos && npm install && npm run build && cd ../..
firebase deploy --only functions:caspian-pos

Nothing else changes for a consumer site. If your code imported readStorageMode,
writeStorageMode, readPrinterTransport or writePrinterTransport, delete those calls —
see Removed.

Fixed

• An offline sale with no leased numbers left printed a blank receipt number.
  PosSaleQueue.capture returns a device-local reference for exactly this case and
  PosQueuedCloudAdapter was discarding it, so the customer got a slip with no identifier
  at all. The reference is now used and labelled as provisional, on screen and on the
  printed receipt.
• A sale interrupted mid-send was never retried and never cleared. send() marks a
  sale sending before the call; a reload or a closed tab left it there permanently —
  drain() only picks up held, pruneSent() only removes sent, and the held-sales
  page offers Retry on blocked alone. The queue now sweeps sending back to held once
  per session, before the online check so the count is right even offline.
• Receipt lines could disagree with the receipt total. Lines and subtotal came from the
  open ticket while the total came back from the commit, so a catalogue edit mid-sale
  printed a slip whose own lines did not add up to its own total. commitSale now returns
  what was charged and the receipt is built from that.
• An online sale burnt a leased receipt number the server never honoured.
  PosCloudAdapter was not forwarding the receipt claim (or capturedByUid /
  capturedByName) to the callable, so the ordinal was spent locally while the server
  allocated a different number from the counter. Leases drained at one number per sale and
  numbering developed permanent gaps.
• Typing into the register's quick-add dialogs fired phantom barcode scans. The
  keyboard wedge was silenced only for the tender phase, which could not see the product
  and person dialogs the POS header opens outside PosRegister. It now detects any open
  dialog from the DOM, so consumer-added dialogs are covered too.
• 1,234.50 was read as 1.234 at the tender screen. String.replace with a string
  argument replaces only the first match, so a grouping separator produced two decimal
  points and parseFloat stopped at the second. On the tendered field that is wrong change
  handed to a customer.
• The register, the connection pill and the held-sales page each built their own
  outbox. They shared IndexedDB so no sale was lost, but capture() and markSent()
  notified an instance nobody was subscribed to, so the held-sales badge only moved on a
  30-second timer and paused — in-memory state — could never be observed by the pill.
  There is now one adapter, provided by PosShell.
• Backups silently dropped custom roles. LOCAL_BACKUP_VERSION is 2 and carries
  roles; v1 files still restore. parseLocalBackup also validates sales is an array,
  which it never did while restoreLocalBackup iterated it.
• "0 receipt numbers left" could never be cleared. The low-numbers warning fired on
  leasedRemaining === 0, which is also a healthy till before its first lease and a store
  with no functions-pos deployment. Lease failure is now tracked separately and reported
  as "Cannot reserve receipt numbers".
• The Math.random fallback in randomId() had no length floor, and the server requires a
  sale id of at least eight characters.

Added

• Line discounts have a control at last. usePosTicket.setLineDiscount was plumbed
  end to end — cloud payload, priceLocalSale, commitPosSale validation, receipt
  renderer — with nothing calling it, so the ticket's discount row and the receipt's
  per-line discount were unreachable. Each ticket line now has a markdown button.
• PosAdapterProvider / usePosAdapter, the shared register storage seam.
• PosSoldLine — a line as it was charged, distinct from the scanned PosSaleLine.
• summariseSoldLines and parseAmount are exported, both pure and both checked by
  scripts/check-standalone.mjs.

Removed

• desktop/ and its build workflow. The Tauri shell that bundled the register for
  Windows is gone; the till is installed from Chrome or Edge with the register's own
  Install button. Existing desktop/v* releases stay on GitHub but are no longer built or
  documented, and the POS manual's Windows-installer section has been deleted. Standalone
  mode itself (<CaspianStoreProvider standalone>, PosLocalAdapter, the local back
  office) is untouched and still exported — it simply has no first-party packaged delivery.
• readStorageMode, writeStorageMode, readPrinterTransport, writePrinterTransport
  and idbCountByIndex. Nothing called any of them: the printer control is hard-coded to
  the browser transport until the ESC/POS paths ship, and the storage mode is derived by
  resolvePosStorageMode rather than stored.
• promoCode from the standalone commit path. priceLocalSale never applied a promo, so
  the field recorded a claim nothing honoured.

Changed

• PosQueuedCloudAdapter takes its queue as a constructor argument instead of building one.
• PosCommittedSale gains optional lines and provisionalReceipt.