build(docker): reliable apt mirror and correct build context

- The default deb.debian.org Cloudflare CDN throttled to ~150 kB/s from
  this network and repeatedly dropped the gcc-12/cpp-12 fetch, failing
  the image build twice. Switch apt to mirror.yandex.ru and add
  Acquire retry/timeout options so the system-dependency layer
  (OCRmyPDF, Tesseract rus+eng, Ghostscript, qpdf) builds reliably.
- Copy pyproject.toml, README.md, alembic.ini and the app/scripts
  packages before "pip install -e ." so hatchling's editable build can
  validate the readme and packages (previously failed with
  "Readme file does not exist: README.md").
- Drop README.md from .dockerignore so the build context includes it.
- Ignore local preview launch config (frontend/.claude, .claude/launch.json).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker/Dockerfile

@@ -6,8 +6,19 @@ ENV PYTHONUNBUFFERED=1 \
     PIP_DISABLE_PIP_VERSION_CHECK=1 \
     DEBIAN_FRONTEND=noninteractive
 
+# Switch apt to a faster mirror (Yandex) before installing. The default
+# deb.debian.org Cloudflare CDN throttles to ~150 kB/s from some networks,
+# stalling the build on gcc-12/cpp-12; Yandex serves consistently faster.
+RUN sed -i 's|deb.debian.org|mirror.yandex.ru|g' /etc/apt/sources.list.d/debian.sources 2>/dev/null \
+ || sed -i 's|deb.debian.org|mirror.yandex.ru|g' /etc/apt/sources.list 2>/dev/null \
+ || true
+
 # System deps for OCRmyPDF + Tesseract (rus+eng) + Ghostscript + qpdf + image libs
-RUN apt-get update && apt-get install -y --no-install-recommends \
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends \
+        --fix-missing -o Acquire::Retries=10 \
+        -o Acquire::http::Timeout=180 \
+        -o Acquire::https::Timeout=180 \
         build-essential \
         curl \
         ca-certificates \
@@ -33,14 +44,15 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /app
 
-COPY pyproject.toml /app/pyproject.toml
-
-RUN pip install --upgrade pip wheel setuptools && \
-    pip install -e .
-
+# Copy the metadata + package payload BEFORE pip install. hatchling validates
+# README.md and the [packages] entries (app, scripts) at editable-install time;
+# missing files cause `Readme file does not exist` even with `pip install -e .`.
+COPY pyproject.toml README.md alembic.ini /app/
 COPY app /app/app
 COPY scripts /app/scripts
-COPY alembic.ini /app/alembic.ini
+
+RUN pip install --upgrade pip wheel setuptools \
+ && pip install -e .
 
 RUN mkdir -p /data/input /data/work