v1.21.0: pre-allocation and POS phone orders

"Pre-allocation and POS phone orders" release. Two threads.

Admin-created and marketplace-inbound sales orders now reserve inventory at create time instead of leaving stock claimable until a picker batches the order, and the picking flow was taught to handle a line that arrives already reserved. On top of that reservation work, POS checkout gains a phone-order path: a phoned-in order is paid at the register but enters the warehouse pick queue with a real structured ship-to, reserving stock rather than decrementing it.

Mobile. Zero mobile/ diffs on this release. The current mobile build (version 1.19.0, versionCode 9) remains current; no new APK for v1.21.0.

Added

• Inventory pre-allocation for admin SOs (#396): POST /admin/sales-orders now follows each line insert with a greedy reservation walk -- it locks the available inventory rows for the line's (item_id, warehouse_id) FOR UPDATE, takes from the fullest bin first, and bumps quantity_allocated until the line is satisfied or stock is exhausted. The order no longer sits OPEN with quantity_allocated=0 until a picker batches it, closing the window where POS sales and concurrent inbound orders could claim the same on-hand pool. Partial reservation is allowed: a short warehouse still creates the SO and the picker handles the short at fulfillment. A manual PATCH /admin/sales-orders/<so_id>/lines/<so_line_id>/allocation knob (signed delta, clamped to [quantity_picked, quantity_ordered]) is surfaced as a minus/plus stepper on the Allocated cell of the SO line table.
• POS phone orders (#397): POS checkout gains an is_phone_order flag (default false; the counter-sale contract is preserved). A phone order creates the SO at status=OPEN with shipped_at NULL and reserves each line via quantity_allocated instead of decrementing quantity_on_hand, so it enters the existing pick queue and the unit stays in its bin until the picker removes it. Checkout accepts an optional customer (customer_name / customer_phone / customer_email) and a structured shipping_address object; on a phone order the structured fields persist to the sales_orders.shipping_address_* columns so the picking ticket renders a real label without a cross-system lookup, while the flat ship_address stays as the floor-screen mirror. order_origin is now wire-driven (the POS sends "POS" / "Phone Order" verbatim; older clients that omit it land as NULL). POS sales-order numbers drop the redundant prefix: SO-POS-<n> becomes POS-<n> and SO-POS-REF-<n> becomes POS-REF-<n>.

Changed

• Pickable pre-reserved lines (#396): a sales-order line can now reach picking already fully reserved -- from pre-allocation, POS phone-order checkout, or a stranded prior allocation. The coverage and allocation passes keyed on quantity_ordered > quantity_allocated, so such a line produced zero pick_tasks and stranded every order in the batch. The picking flow now normalizes each line's standing reservation to its picked floor before planning (releasing quantity_allocated - quantity_picked back to inventory inside the one transaction), then re-reserves and tasks it like any fresh line. Applies to create_pick_batch and wave_create.

No new migrations.