add CLAUDE.md for Claude Code guidance

[roninsightrx]

No description provided.

[mccarthy-m-g]

A couple snapshot tests for VPC plots are failing in CI, probably due to vpc being updated, so we just need to update the snaps.

══ Failed tests ════════════════════════════════════════════════════════════════
── Failure ('test-run_vpc.R:19:3'): Basic vpc with vanco data + model works ────
Snapshot of `testcase` has changed.

Backtrace:
    ▆
 1. └─vdiffr::expect_doppelganger("nm_vanco VPC", plot(vpc_vanc, show = list(obs_dv = TRUE))) at test-run_vpc.R:19:3
 2.   ├─base::withCallingHandlers(...)
 3.   └─testthat::expect_snapshot_file(...)
── Failure ('test-run_vpc.R:43:3'): Busulfan vpc with vanco data + model works ──
Snapshot of `testcase` has changed.

Backtrace:
    ▆
 1. └─vdiffr::expect_doppelganger(...) at test-run_vpc.R:43:3
 2.   ├─base::withCallingHandlers(...)
 3.   └─testthat::expect_snapshot_file(...)

── Snapshots ───────────────────────────────────────────────────────────────────
To review and process snapshots locally:
* Run `testthat::snapshot_download_gh("InsightRX/mipdeval", "23606096565")` to download snapshots.
* Run `testthat::snapshot_accept()` to accept all changes.
* Run `testthat::snapshot_review()` to review all changes.
[ FAIL 2 | WARN 0 | SKIP 0 | PASS 149 ]
Error:
! Test failures.
Execution halted

[mccarthy-m-g]

I also asked Claude for suggestions on what to use claude.md for:

claude.md (or CLAUDE.md) is a configuration file used with Claude Code — Anthropic's agentic coding tool. It serves as a persistent instruction file that tells Claude how to behave within a specific project or environment.

Here's what it's typically used for:

Project context — Describing what the project is, its architecture, and key conventions Claude should be aware of.

Custom instructions — Defining rules Claude should follow, like coding style preferences, naming conventions, or which tools/commands to use.

Common commands — Documenting frequently used build, test, or deployment commands so Claude can run them correctly.

Off-limits areas — Specifying files, directories, or actions Claude should avoid.

Workflow guidance — Explaining how the team works, branching strategies, PR processes, etc.

I think we could add custom instructions (e.g., naming conventions and tools to use when writing unit tests), and off-limits areas (it doesn't ever need to read the files in man/) to our file.