feat(api): /api/lead с SQLite и миграциями

db/: better-sqlite3 по DB_PATH (WAL, foreign_keys), миграции через
PRAGMA user_version, схема leads и lead_clarifications по плану.
createApp(deps) с инъекцией базы, часов и notifier (пока no-op, зовётся
после ответа). POST /api/lead: только JSON (415), тело до 16 КБ (413),
validateLead → 400, запись → 201. index.ts: env и graceful shutdown.

apps/api/src/leads.ts

@@ -0,0 +1,26 @@
+import type { ValidLead } from '@kvarta/shared/lead';
+import type { Db } from './db/index.js';
+import type { LeadEvent } from './notifier.js';
+
+export type SaveMeta = { now: Date; userAgent: string | null };
+
+export type SaveResult = { kind: 'created'; event: LeadEvent };
+
+export function saveLead(db: Db, lead: ValidLead, meta: SaveMeta): SaveResult {
+  const { lastInsertRowid } = db
+    .prepare(
+      `INSERT INTO leads (created_at, phone, name, interest, comment, first_touch, last_touch, user_agent)
+       VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
+    )
+    .run(
+      meta.now.toISOString(),
+      lead.phone,
+      lead.name,
+      lead.interest,
+      lead.comment,
+      lead.firstTouch ? JSON.stringify(lead.firstTouch) : null,
+      JSON.stringify(lead.lastTouch),
+      meta.userAgent,
+    );
+  return { kind: 'created', event: { kind: 'lead', leadId: Number(lastInsertRowid) } };
+}