Fix MEDIUM findings from 2026-09-24 maintenance review

- Backend retries DB connection at startup (up to 180s) so host reboots
  no longer crash-loop it; add backend and frontend healthchecks
- Docker log rotation (json-file 10m x 3) on all services
- ntfy alerts use X-Real-IP (set by nginx after real_ip resolution)
  instead of the client-controlled first X-Forwarded-For entry
- Frontend build on Node 24 LTS with package-lock.json + npm ci;
  axios 1.20.0, vite 5.4.21
- README: backup/restore/rollback runbook, real-IP proxy trust notes
- Release-Notes/v1.1.md; version 1.1.0

Co-Authored-By: Claude Opus 5.5 <[email protected]>

frontend/Dockerfile

@@ -1,10 +1,10 @@
 # Stage 1: Build Vue.js app
-FROM node:20.20.1-alpine AS builder
+FROM node:24.21.0-alpine AS builder
 
 WORKDIR /app
 
-COPY package.json package-lock.json* ./
-RUN npm install
+COPY package.json package-lock.json ./
+RUN npm ci
 
 COPY . .
 RUN npm run build