deploy(docker): utente non root e versioni base pinnate (#38)

Punto 1: useradd -u 10001 app, chown /app (+ /app/uploads sul server),
USER app in tutti e tre i Dockerfile. Stesso UID sul server e sul worker
di visione, che condividono il volume uploads in sola lettura (punto 13).

Punto 2: python:3.11.16-slim (server, client), python:3.13.15-slim
(vision), ghcr.io/astral-sh/uv:0.10.9 (versione locale di `uv --version`).
Dockerfile.frontend: TailwindCSS ora si compila in uno stage separato
dall'immagine ufficiale node:20.20.2-bookworm-slim, non più con
`curl | bash` su nodesource nell'immagine finale.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Dockerfile

@@ -1,7 +1,7 @@
-FROM python:3.11-slim AS base
+FROM python:3.11.16-slim AS base
 
 # Install uv (fast Python package manager) from official slim image.
-COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /usr/local/bin/
+COPY --from=ghcr.io/astral-sh/uv:0.10.9 /uv /uvx /usr/local/bin/
 
 # System libs required by WeasyPrint at runtime.
 RUN apt-get update && apt-get install -y --no-install-recommends \
@@ -13,6 +13,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     shared-mime-info \
     && rm -rf /var/lib/apt/lists/*
 
+# Non-root user the app runs as at runtime.
+RUN useradd -u 10001 app
+
 WORKDIR /app
 
 # Copy lockfile + project metadata first to maximize Docker layer cache.
@@ -27,7 +30,10 @@ RUN uv sync --frozen --no-dev --extra server
 COPY src/ ./src/
 
 # Uploads directory (mounted as a volume in production).
-RUN mkdir -p /app/uploads/images /app/uploads/pdfs /app/uploads/logos /app/uploads/reports
+RUN mkdir -p /app/uploads/images /app/uploads/pdfs /app/uploads/logos /app/uploads/reports \
+    && chown -R app:app /app
+
+USER app
 
 EXPOSE 8000