feat: leads capture API with PostgreSQL backend

Bun + Hono API service for capturing email subscribers across
multiple projects. Supports subscribe/unsubscribe, admin stats,
and deduplication per email+project pair.

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

Dockerfile

@@ -0,0 +1,8 @@
+FROM oven/bun:1.3-alpine
+WORKDIR /app
+COPY package.json bun.lock* ./
+RUN bun install --frozen-lockfile 2>/dev/null || bun install
+COPY src ./src
+ENV NODE_ENV=production
+EXPOSE 3400
+CMD ["bun", "run", "src/index.ts"]