fix(cookbook): redirect pip cache away from $HOME (#1219)

[PrabinDevkota]

Summary

Redirect pip wheel/build cache and temp dirs away from $HOME so Cookbook dependency installs and pip install -r requirements.txt do not fill a small home partition (No space left on device). Complements the existing --no-cache-dir Cookbook path (#1477) by also covering Docker, native install scripts, and wheel build temps via TMPDIR.

Target branch

• This PR targets dev, not main. All PRs land in dev; main is curated by the maintainer at each release. If your PR is on main by accident, click "Edit" on this PR and change the base.

Linked Issue

Fixes #1219

Type of Change

• Bug fix (non-breaking — fixes a confirmed issue)
• New feature (non-breaking — adds new behaviour)
• Breaking change (changes or removes existing behaviour)
• Refactor / cleanup (behaviour unchanged)
• Documentation only
• CI / tooling / configuration

Checklist

• I searched open issues and open PRs — this is not a duplicate.
• This PR targets dev
• My changes are limited to the scope described above — no unrelated refactors or whitespace changes mixed in.
• I actually ran the app (docker compose up or uvicorn app:app) and verified the change works end-to-end. Type-checks and unit tests are not enough.

How to Test

1. Confirm the focused unit tests pass:

   python -m pytest tests/test_cookbook_helpers.py -k pip_build -q
   python -m py_compile routes/cookbook_helpers.py routes/cookbook_routes.py

2. Native install path: with a tight home disk (or by inspecting env), run a local Cookbook dependency install or pip install -r requirements.txt and verify PIP_CACHE_DIR / TMPDIR point under ./data/ (or /app/data/ in Docker).
3. Docker: docker compose config (or inspect the running container env) should show PIP_CACHE_DIR=/app/data/pip-cache and TMPDIR=/app/data/tmp by default; entrypoint creates those dirs on the data volume.
4. Optional regression: remote Cookbook serve/download scripts should not inject the local pip-cache exports (only local bash runners do).

Visual / UI changes — REQUIRED if you touched anything that renders

N/A — no UI/rendering changes.

[pewdiepie-archdaemon]

Thanks, this is pointed at a real issue from #1219 and the intended file list makes sense, but the branch is currently stale against main. The two-dot diff still includes already-merged/unrelated files like routes/model_routes.py, src/url_safety.py, static/app.js, static/js/sessions.js, and multiple endpoint/sidebar tests.

Can you rebase onto current main and push again so the two-dot diff contains only the intended files? Expected scope from the PR file list is:

• .env.example
• CONTRIBUTING.md
• README.md
• docker-compose.yml
• docker/entrypoint.sh
• routes/cookbook_helpers.py
• routes/cookbook_routes.py
• start-macos.sh
• tests/test_cookbook_helpers.py

Also, minor naming note: the PR changes Cookbook install runtime behavior, not only docs, so a fix(cookbook) title would describe it more accurately than docs(install). Once rebased, the focused checks I would run are the cookbook helper tests plus py_compile for the touched route/helper files.