feat(floor): the shop floor, and a sale recorded against a visit

Two surfaces a merchant currently has no way to reach, and the BFF routes
behind them.

/floor is the only screen in this console aimed at somebody standing behind
a counter: who walked in, who is being served, and by whom. A visit is
claimed with attend, handed back with release, and closed with complete.
Claiming is single-winner — the platform decides, and a second person
tapping the same customer gets 409 CUSTOMER_ALREADY_TAKEN rather than a
silent overwrite. That was verified against a live platform: eight
concurrent claims, exactly one winner.

Naming a walk-in posts to /api/customers, which is the same permission as
PUT /api/visitors/{id}/profile upstream — attaching a name and a phone
number to a face is the floor's job, not a manager's.

Sale entry sits on the floor because that is where a sale happens. Lines
carry an intent, purchased or enquired, so a shop can record what somebody
asked about and did not buy; only purchased lines are billed. Money is
integer paise end to end and formatPaise is the only place it becomes
rupees — a float round-trip through the BFF was rejected once already and
must not come back.

Every write carries an idempotency key minted per dialog, so a double tap,
a timeout retry and a resubmit collapse into one sale rather than three.
Proven live: a replayed key returns 200 already_processed with the original
sale id.

/commerce gains the real list of those sales, replacing nothing invented —
it reads GET /api/sales and opens a detail view per row.

── What this does NOT do ────────────────────────────────────────────────
No mock, demo or placeholder data anywhere in it. Every figure comes off a
payload; an empty floor renders an empty state and says so.

── Known: the deployed backend does not serve these yet ─────────────────
/api/floor/visits, /api/customers, /api/sales and the three visit actions
all answer 404 on mcp.loyaly.ai today, which runs a build older than this
repository's first commit. Until that backend ships, /floor and the sales
panel will show error states, and the Floor nav entry points at a page that
cannot load its data. Committed deliberately so the two halves can be
deployed together rather than drifting further apart.

staff -> /floor has been the committed destination since 697b0d9; this is
the page it was always pointing at.

Verified: tsc clean, production build clean, lint unchanged at the existing
baseline. Exercised against a live local platform for all three roles —
attend/release/steal-prevention, customer creation, sale creation and
idempotent replay, and two-tenant isolation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0161AMotQ8FxGPZ9gFGb5wiK

src/shared/layouts/workspace/nav-config.ts

@@ -14,6 +14,7 @@ export interface NavEntry {
  */
 export const PRIMARY_NAV: NavEntry[] = [
   {label: 'Dashboard', href: '/dashboard', icon: ICONS.dashboard},
+  {label: 'Floor', href: '/floor', icon: ICONS.visitors},
   {label: 'Commerce', href: '/commerce', icon: ICONS.commerce},
   {label: 'Store', href: '/stores', icon: ICONS.stores},
   {label: 'Lyts', href: '/lyts', icon: ICONS.lyts},