Add multi-line sale builder with pending-draft safeguard

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/server/schema.sql

@@ -54,3 +54,28 @@ CREATE INDEX IF NOT EXISTS idx_parts_barcode       ON parts(barcode);
 CREATE INDEX IF NOT EXISTS idx_parts_category      ON parts(category_id);
 CREATE INDEX IF NOT EXISTS idx_movements_part      ON stock_movements(part_id);
 CREATE INDEX IF NOT EXISTS idx_movements_created   ON stock_movements(created_at);
+
+CREATE TABLE IF NOT EXISTS invoices (
+  id           INTEGER PRIMARY KEY AUTOINCREMENT,
+  status       TEXT NOT NULL CHECK(status IN ('pending','saved')) DEFAULT 'pending',
+  total_dirams INTEGER NOT NULL DEFAULT 0,
+  notes        TEXT,
+  created_at   TEXT NOT NULL DEFAULT (datetime('now')),
+  saved_at     TEXT
+);
+
+CREATE TABLE IF NOT EXISTS invoice_lines (
+  id                 INTEGER PRIMARY KEY AUTOINCREMENT,
+  invoice_id         INTEGER NOT NULL REFERENCES invoices(id) ON DELETE CASCADE,
+  part_id            INTEGER REFERENCES parts(id) ON DELETE SET NULL,
+  label              TEXT,
+  quantity           INTEGER NOT NULL CHECK(quantity > 0),
+  unit_price_dirams  INTEGER NOT NULL DEFAULT 0,
+  affects_inventory  INTEGER NOT NULL DEFAULT 1,
+  sort_order         INTEGER NOT NULL DEFAULT 0,
+  created_at         TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
+CREATE INDEX IF NOT EXISTS idx_invoice_lines_invoice ON invoice_lines(invoice_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_invoices_one_pending
+  ON invoices(status) WHERE status = 'pending';