Add macOS setup guide

[kocaemre]

Summary

• Add docs/setup/macos.md with tested prerequisite checks for modern Bash, Node/Corepack, Python, Docker Compose, and Go Task.
• Explain how #!/usr/bin/env bash resolves Bash from PATH, including Apple Silicon and Intel Homebrew prefixes.
• Link the macOS setup guide from the root README.
• Add a focused Node test that guards the README link and the required safety/prerequisite content.

Issue Or Context

• Related issue: Fixes [Docs] Add tested macOS prerequisites and modern Bash troubleshooting #56
• First-time contributor?: No
• Area changed: README, docs, local tooling guidance

Verification

• I ran the narrowest check that proves this change.
• I ran task doctor when local tooling, env files, Docker services, or setup docs changed.
• I ran pnpm ci:local for shared code, CI, dependency, build, or release workflow changes, or documented the narrower check below.
• Dependency changes are intentional, reflected in pnpm-lock.yaml, and any audit suppression changes include an expiry date.
• UI screenshots or recordings are attached for product UI changes, or this PR has no product UI surface.
• Environment changes are documented in the relevant .env.*.example, workflow variable notes, or README section.
• I added broader checks if this touches shared code, auth, billing, database models, runtime agent behavior, or production UI.
• For docs-only changes, I reviewed links, commands, and provider-credential boundaries.

Command or review evidence:

# RED before adding the guide/link:
node --test tests/macos-setup-doc.test.mjs
# failed because README did not link ./docs/setup/macos.md and docs/setup/macos.md did not exist

node --test tests/macos-setup-doc.test.mjs
node --test tests/*.test.mjs
pnpm exec prettier --check README.md docs/setup/macos.md tests/macos-setup-doc.test.mjs
git diff --check
task doctor

Results:

• tests/macos-setup-doc.test.mjs: 2/2 passed.
• Root Node tests: 33/33 passed.
• Prettier check passed.
• git diff --check passed.
• task doctor exited 0. It reported Bash/Task/Go/Node/Corepack/Python/Docker checks OK and warned only that local Postgres/Redis were not running, which is expected before task docker:up.

pnpm ci:local was not run because this is a docs/setup-guide PR with a focused documentation regression test and no runtime, dependency, build, Docker image, Python, auth, billing, or database changes.

No dependency, audit suppression, product UI, or env-template changes are included.

Launch And Positioning Guardrails

• Public copy keeps the open-source Retell alternative story focused on control, self-hosting, privacy review, cost visibility, and extensibility.
• Competitive comparisons explain tradeoffs without attacking competitors.
• This PR does not invent screenshots, metrics, benchmarks, customers, compliance claims, provider partnerships, or production readiness claims.
• Provider requirements are explicit when real calls, billing, OAuth, email, storage, or deployment need live credentials or product decisions.

Screenshots Or Recordings

No product UI surface.

Maintainer Review Notes

• I verified the commands on Linux in this PR environment. Per [Docs] Add tested macOS prerequisites and modern Bash troubleshooting #56, a maintainer still needs to record the exact macOS version/CPU used for final macOS verification before treating the guide as tested on macOS.