Drop compromised eMudhra roots from outbound TLS trust (#36)

Outbound TLS in this image still trusted the compromised eMudhra roots (`emSign ECC Root CA - G3` and `Comodo AAA Services`).

- Image install now upgrades `ca-certificates` and regenerates the trust bundle.
- `certifi` is locked at 2026.10.23, which drops those roots for `requests` and `httpx`.

Merge this, then redeploy prod.

Reviewed-on: #36

Dockerfile

@@ -9,7 +9,8 @@ ENV PYTHONDONTWRITEBYTECODE=1 \
 WORKDIR /app
 
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends libpq5 \
+    && apt-get install -y --no-install-recommends ca-certificates libpq5 \
+    && update-ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
 COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv