Improve developer onboarding with one-line install and doctor command

[Jing-yilin]

Summary

Implement the developer onboarding improvements from the Developer Onboarding Spec, and align them with the Raycast extension release workflow.

Specs:

• Developer onboarding: https://markshare.to/@yilinjing/perch-developer-onboarding-spec-sf2ZhgR
• Raycast extension spec in repo: markshare/raycast-extension-spec.md

Updated Scope

Developer onboarding

• One-line remote installer via:

  curl -fsSL https://raw.githubusercontent.com/ReScienceLab/Perch/main/install.sh | sh

• Download prebuilt perch CLI from latest GitHub Release by default.
• Initialize ~/.config/perch/sessions.json and ~/.config/perch/config idempotently.
• Install /perch commands/skills for detected agents.
• Add perch doctor setup diagnostics.
• Publish prebuilt macOS CLI artifacts and checksums.
• Update README with a 60-second Quick Start.

Raycast release dependency

The Raycast extension should be publishable only after the CLI onboarding path is reliable, because Store users need a simple prerequisite path before using Search/Add Sessions.

Raycast-specific requirements:

• Extension README must state the prerequisite one-line Perch CLI install.
• Empty/error states must guide users to install Perch or run perch doctor.
• Mutation actions should call the installed perch binary rather than reimplementing store writes.
• Release checklist must include npm run lint, npm run build, icon, screenshots, CHANGELOG, and npm run publish / npx ray publish PR flow to raycast/extensions.

Non-goals

• No Perch.app installation or release artifact required.
• No DMG packaging.
• No launch-at-login.
• No signing/notarization for this issue.
• Raycast extension should not become an installer; it depends on the CLI installer.

Acceptance Criteria

Installer / CLI

• One-line remote installer works without cloning the repo.
• Installer uses latest GitHub Release CLI by default.
• Installer supports local repo mode and remote curl | sh mode.
• Installer initializes config/session storage idempotently.
• Installer installs /perch commands for detected agents.
• Installer fails clearly on unsupported platforms or missing release artifacts.
• perch doctor reports actionable diagnostics and appropriate exit codes.
• perch doctor --json is available for automation.
• Release workflow publishes macOS arm64 and x86_64 CLI binaries plus checksums.
• README starts with a 60-second Quick Start.

Raycast publishing readiness

• raycast-extension/README.md documents one-line CLI install, default sessions path, and perch doctor troubleshooting.
• Raycast empty/error states mention the one-line installer or perch doctor where relevant.
• Raycast mutation actions use configured/resolved perch CLI path.
• raycast-extension passes npm run lint and npm run build.
• Raycast Store assets are prepared: custom 512x512 icon, CHANGELOG, and at least 3 screenshots.
• npm run publish / npx ray publish can create the Raycast Store PR after prerequisites are met.