[Code scan] Make Docker builds use the checked-out source instead of cloning mutable upstream

This issue is part of a Codex global repository scan.

Problem:
Both Dockerfiles ignore the local build context and run `git clone https://github.com/deepmodeling/DeePTB.git`, then install whatever branch state GitHub serves at build time.

Code references:
https://github.com/deepmodeling/deeptb/blob/86c60c73996f0dd961c3138f2e88424382cb734e/Dockerfile#L33-L35
https://github.com/deepmodeling/deeptb/blob/86c60c73996f0dd961c3138f2e88424382cb734e/Dockerfile.main#L34-L36

Impact:
Building this commit can produce an image from different source code, and local changes cannot be tested in Docker. This makes Docker builds non-reproducible for PRs and release commits.

Suggested fix:
Use `COPY . /DeePTB` and install from the checked-out source, or pin the clone to the intended commit/tag via build args.

Start by reading Dockerfile and Dockerfile.main at the referenced build steps, then build the images from the checked-out repository context. Verify that the image installs the local source rather than cloning mutable upstream code, and that local or commit-specific changes are reflected in the resulting image.

Written by the indexing model from the issue text.