[glm-grade=A-] refactor: extract /api/v1/version into routes/version.js + npm ci build

Companion to ff92706 (drift test fix). The inline handler moves to a
module exporting { buildRouter, getVersion, getName }, pre-built once
at startup and mounted bare on apiRouter — the exact shape the drift
test walker now recognizes. Dockerfile builder stage switches to
npm ci --omit=dev for deterministic builds. Tests: 12/12 across the
three new/updated suites; full suite 1837/1837.

dashcaddy-api/Dockerfile

@@ -1,10 +1,10 @@
-# ── Build stage: install all deps (including devDeps for build tooling) ──────
+# ── Dependency stage: deterministic production-only install ────────────────
 FROM node:20.11.1-alpine3.19 AS builder
 
 WORKDIR /app
 
 COPY package*.json ./
-RUN npm install
+RUN npm ci --omit=dev
 
 # ── Production stage: only production deps + source ──────────────────────────
 FROM node:20.11.1-alpine3.19
@@ -22,6 +22,7 @@ COPY *.js ./
 COPY src/ ./src/
 COPY routes/ ./routes/
 COPY openapi.yaml ./
+COPY package.json ./
 
 # VERSION file holds the short git SHA the image was built from.
 COPY VERSION ./