feat: add client disable/deletion with soft-delete (#67)

Add soft-delete support for clients: disable is the default action
(hiding from client list and booking flow), with permanent deletion
requiring explicit type-to-confirm. Disabled clients remain in
reporting and can be re-enabled by staff.

- Add client_status enum (active/disabled) and disabled_at column
- API defaults GET /api/clients to active-only, ?includeDisabled=true shows all
- PATCH /api/clients/:id accepts status field for disable/enable
- DELETE requires ?confirm=true query param
- Booking flow skips disabled clients
- Frontend: show disabled toggle, disable/enable buttons, delete confirmation modal

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/db/migrations/0009_client_soft_delete.sql

@@ -0,0 +1,6 @@
+-- Add client status (soft-delete support)
+CREATE TYPE "client_status" AS ENUM ('active', 'disabled');
+
+ALTER TABLE "clients"
+  ADD COLUMN "status" "client_status" NOT NULL DEFAULT 'active',
+  ADD COLUMN "disabled_at" timestamp;