Fix Dockerfile COPY destination path for buildx compatibility

[Copilot]

Docker buildx fails to resolve the build context when copying directories without explicit ./ prefix in multi-stage builds, resulting in "/README.md": not found errors.

Changes

• Dockerfile: Changed COPY checkdmarc/ checkdmarc/ to COPY checkdmarc/ ./checkdmarc/ to explicitly specify the destination path relative to WORKDIR

The explicit ./ prefix ensures Docker buildx correctly resolves file paths in the build context during multi-stage builds.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Docker & build</issue_title>
<issue_description>using your Dockerfile :

docker buildx build --file Dockerfile --tag check_dmarc .

[+] Building 1.2s (9/12) docker:default
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 629B 0.0s
=> [internal] load metadata for docker.io/library/python:3.13-slim 1.2s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> CANCELED [build 1/6] FROM docker.io/library/python:3.13-slim@sha256:baf66684c5fcafbda38a54b227ee30ec41e40af1e4073edee3a7110a417756ba 0.0s
=> => resolve docker.io/library/python:3.13-slim@sha256:baf66684c5fcafbda38a54b227ee30ec41e40af1e4073edee3a7110a417756ba 0.0s
=> => sha256:baf66684c5fcafbda38a54b227ee30ec41e40af1e4073edee3a7110a417756ba 10.37kB / 10.37kB 0.0s
=> => sha256:6ea5d7c9376f1f4fcb9a41b4250f8c2667865d86aae925adfba67f832ed0584c 1.75kB / 1.75kB 0.0s
=> => sha256:22feee3156404e79c24866d7d022bbba8542c08365666092f71a0deed6886c09 5.53kB / 5.53kB 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 2B 0.0s
=> CACHED [build 2/6] WORKDIR /app 0.0s
=> CACHED [build 3/6] RUN pip install hatch 0.0s
=> ERROR [build 4/6] COPY checkdmarc/ checkdmarc/ 0.0s
=> ERROR [build 5/6] COPY README.md pyproject.toml ./ 0.0s

[build 4/6] COPY checkdmarc/ checkdmarc/:
[build 5/6] COPY README.md pyproject.toml ./:

Dockerfile:15

13 |
14 | COPY checkdmarc/ checkdmarc/
15 | >>> COPY README.md pyproject.toml ./
16 |
17 | RUN hatch build

ERROR: failed to build: failed to solve: failed to compute cache key: failed to calculate checksum of ref dec753e6-0d6d-4cd1-82fb-e0fdb6f72ec7::0p0kcne1uuyy6nfc6zmvchwyz: "/README.md": not found
</issue_description>

<agent_instructions>Fix the Dockerfile to resolve the error</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Docker & build #227

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