Fix duplicate venv copy in server Dockerfile template

[ritvik412]

Fixes #1021

Problem

openenv init generates a Dockerfile whose final stage copies the built
virtualenv twice: once explicitly, and once again implicitly because uv sync
places .venv inside /app/env, and the next layer copies /app/env
wholesale — nesting a second full copy of the venv inside it. This roughly
doubles the image size (confirmed via dive in the issue: two ~523-524MB
layers for what should be one).

Fix

• Move .venv out of /app/env in the builder stage, before the final
  stage's copies happen, so the wholesale COPY --from=builder /app/env /app/env no longer contains a nested venv.
• Recreate a .venv symlink inside /app/env in the runtime stage (pointing
  at the single real copy at /app/.venv) so tooling that expects the venv
  alongside the project (e.g. uv run) still works, with no second physical
  copy on disk.
• Applied identically to src/openenv/cli/templates/openenv_env/server/Dockerfile
  and .claude/skills/generate-openenv-env/assets/openenv_env_template/server/Dockerfile,
  since these two files were already kept byte-for-byte identical (aside from
  license header) and would otherwise drift.

Testing

Built a fresh env from the fixed template (openenv init + docker build) and
confirmed via docker history that the venv is now copied once, not twice:

---

Note

Low Risk
Build-only Dockerfile template change with no runtime application logic; behavior is intended to stay the same aside from smaller images.

Overview
Fixes roughly doubled Docker image size for environments built from openenv init by stopping the server Dockerfile from shipping the same virtualenv twice.

In the builder stage, .venv is moved from /app/env/.venv to /app/.venv before the runtime stage copies /app/env wholesale, so that layer no longer embeds a second full copy of the venv alongside the explicit COPY to /app/.venv. The runtime stage adds a symlink /app/env/.venv → /app/.venv so tools that expect a venv next to the project (e.g. uv run) still work without a second on-disk copy.

The same change is applied in both src/openenv/cli/templates/openenv_env/server/Dockerfile and .claude/skills/generate-openenv-env/assets/openenv_env_template/server/Dockerfile to keep them aligned.

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