feat(db): add SQLite foundation for FCM registration storage

Introduce better-sqlite3 and a schema-init module so we can migrate off JSON storage without changing runtime behavior yet.

Dockerfile

@@ -1,6 +1,8 @@
 # ---- build stage: install everything, type-check + compile to JS ----
 FROM node:22-alpine AS build
 
+RUN apk add --no-cache python3 make g++
+
 RUN corepack enable && corepack prepare pnpm@11.4.0 --activate
 
 WORKDIR /app
@@ -15,6 +17,8 @@ RUN pnpm build
 # ---- runtime stage: prod deps + compiled JS only, no tsx/esbuild ----
 FROM node:22-alpine AS runtime
 
+RUN apk add --no-cache python3 make g++
+
 RUN corepack enable && corepack prepare pnpm@11.4.0 --activate
 
 WORKDIR /app