docs: make the demo tape portable

[Steel-tech]

The recording tape hardcoded /Users/vics/..., which is unreproducible on anyone else's machine and a personal detail to publish. Caught while auditing the repo ahead of making it public.

Now uses $HOME for the cargo bin path, and BULLPEN_HOME to isolate the demo store rather than overriding HOME — which is what BULLPEN_HOME is for, and didn't exist when this tape was written.

No effect on the committed GIF; this only matters when re-recording with vhs docs/media/bullpen-agents.tape.

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Summary by CodeRabbit

• Documentation
  • Updated the demo command to use a portable Cargo binary path.
  • Configured the demo to run with an isolated temporary home directory.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c3016c3a-1698-4699-a013-27f2c90b94b3

📥 Commits

Reviewing files that changed from the base of the PR and between 2d445fb and e0de22d.

📒 Files selected for processing (1)

• docs/media/bullpen-agents.tape

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📝 Walkthrough

Walkthrough

The demo shell command now resolves Cargo from $HOME and stores Bullpen state under /tmp/bpdemo/home.

Changes

Bullpen demo setup

Layer / File(s)	Summary
Portable demo environment docs/media/bullpen-agents.tape	The terminal setup command replaces the hardcoded Cargo path and HOME assignment with $HOME/.cargo/bin and BULLPEN_HOME=/tmp/bpdemo/home.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• StructuPath/bullpen#10: Uses BULLPEN_HOME to isolate the demo’s Bullpen state directory.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: making the demo tape portable.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/tape-portable

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_{Comment @coderabbitai help to get the list of available commands.}

[Steel-tech]

🤖 Lab Code Review (draft opinion)

No diff provided to review.