docs(CONTRIBUTING): add missing macOS prereqs (Ninja, x86_64 target, …

[aregmii]

Summary

• Adds ninja to the prerequisites table — required by CMake when building the CEF helper on macOS.
• Adds rustup target add x86_64-apple-darwin to the macOS bootstrap snippet — the CEF helper builds a universal binary, so the x86_64 target is needed even on Apple Silicon.
• Adds a macOS platform-notes bullet pointing contributors at the existing scripts/setup-dev-codesign.sh first-run helper.

Problem

Following CONTRIBUTING.md exactly on a clean macOS install fails three times in sequence on pnpm --filter openhuman-app dev:app (Ninja missing, x86_64 target missing, signing identity missing) before reaching a working app. None of these prerequisites are mentioned today.

Solution

Doc-only change to CONTRIBUTING.md. No code, scripts, or behavior changed. The scripts/setup-dev-codesign.sh already exists in the repo — we just reference it from the place a fresh contributor would actually look.

Submission Checklist

• N/A — docs-only change, no behavior to test
• N/A — docs-only change, no code lines under coverage
• N/A — docs-only change, no feature rows affected
• N/A — docs-only change, no feature IDs
• N/A — docs-only change, no external dependencies introduced
• N/A — docs-only change, no release-cut surfaces touched
• Linked issue closed via Closes #1781 in the ## Related section

Impact

Reduces fresh-contributor friction on macOS from "three failed builds, internet-search the errors" to "follow the doc, app boots." No runtime, performance, security, migration, or compatibility implications.

Related

• Closes: docs(CONTRIBUTING): add missing macOS prereqs (Ninja, x86_64 target, codesign script) #1781
• Follow-up PR(s)/TODOs:
  • Fix the partition-list bug in scripts/setup-dev-codesign.sh (the freshly-imported cert needs security set-key-partition-list to grant codesign access without a Keychain dialog every build).
  • Consider adding ripgrep to the prerequisites table — the lint:commands-tokens pre-push step shells out to rg without a presence check.

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AI Authored PR Metadata (required for Codex/Linear PRs)

N/A — Human-authored docs PR.

Linear Issue

• Key: N/A
• URL: N/A

Commit & Branch

• Branch: docs/contributing-setup-macos
• Commit SHA: 70df9119

Validation Run

• N/A — docs-only, no JS/TS changed
• N/A — docs-only, no TS types changed
• N/A — docs-only
• N/A — docs-only, no Rust changed
• N/A — docs-only, no Tauri code changed

Validation Blocked

• command: pre-push hook pnpm rust:check (cargo check --manifest-path src-tauri/Cargo.toml)
• error: exits 101 on the unmodified upstream/main HEAD (commit f583829d); this branch only edits CONTRIBUTING.md, so the failure is inherited from upstream and unrelated to this PR.
• impact: Pushed with --no-verify per CLAUDE.md guidance for hook failures unrelated to the change.

Behavior Changes

• Intended behavior change: None — doc clarification only.
• User-visible effect: Fresh contributors hit zero setup failures on macOS.

Parity Contract

• Legacy behavior preserved: Yes — no runtime code touched.
• Guard/fallback/dispatch parity checks: N/A — no dispatch path touched.

Duplicate / Superseded PR Handling

• Duplicate PR(s): None
• Canonical PR: This one
• Resolution: N/A

Summary by CodeRabbit

• Documentation
  • Updated development setup instructions and prerequisites for macOS builds.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 656ad2b1-9983-4d90-a38f-68ef3879b55a

📥 Commits

Reviewing files that changed from the base of the PR and between 609b6b7 and 70df911.

📒 Files selected for processing (1)

• CONTRIBUTING.md

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📝 Walkthrough

Walkthrough

CONTRIBUTING.md is updated to document three previously undocumented macOS setup requirements: Ninja as a build tool prerequisite, the x86_64-apple-darwin Rust target for CEF universal binary compilation, and a one-time dev codesigning certificate setup using the existing setup script.

Changes

macOS Build Prerequisites and Setup

Layer / File(s)	Summary
macOS build prerequisites and setup documentation CONTRIBUTING.md	Prerequisites table adds Ninja; macOS bootstrap example installs ninja, adds x86_64-apple-darwin Rust target for universal CEF binaries, and references the one-time dev codesigning certificate setup script.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

A rabbit hops through docs so fine,
With Ninja builds and targets aligned,
Now macOS souls won't lose their mind,
With signs to codesign, one step at a time! 🐰✨

🚥 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 accurately summarizes the main change: adding missing macOS prerequisites (Ninja, x86_64 target) to CONTRIBUTING.md documentation.
Linked Issues check	✅ Passed	The PR addresses all three acceptance criteria from issue #1781: adding Ninja to prerequisites, including rustup target add command, and referencing the codesign setup script.
Out of Scope Changes check	✅ Passed	The changes are limited to CONTRIBUTING.md documentation updates related to macOS setup prerequisites, staying within the scope defined by issue #1781.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[senamakel]

thanks for the contribution