Implement developer onboarding and Raycast release readiness

[Jing-yilin]

Summary

Implements issue #2 developer onboarding and Raycast publishing readiness from the raycast-extension branch.

• Adds remote-capable install.sh that installs latest GitHub Release CLI by default, initializes config/session storage, installs detected agent /perch commands, and falls back to local Cargo builds for contributor installs.
• Adds perch doctor and perch doctor --json diagnostics for CLI location, config/session files, agent binaries, and installed commands.
• Adds macOS CLI release workflow for arm64/x86_64 binaries plus SHA-256 checksums.
• Updates README Quick Start and Raycast README/error messages to point users to one-line install and perch doctor.

Validation

• cargo test --manifest-path cli/Cargo.toml
• tests/install.sh
• cd raycast-extension && npm run lint
• cd raycast-extension && npm run build
• perch doctor --json output validates as JSON

Closes #2

[Jing-yilin]

Updated per Raycast/binary dependency best practices and Devin review:\n\n- Installer now downloads and verifies the release .sha256 before executing/installing the CLI.\n- Release workflow now creates the GitHub Release on tag push if it does not already exist, then uploads binaries/checksums.\n- Added installer test coverage for the remote release path and checksum verification.\n\nRevalidated:\n- cargo test --manifest-path cli/Cargo.toml\n- tests/install.sh\n- cd raycast-extension && npm run lint\n- cd raycast-extension && npm run build

[Jing-yilin]

Applied remaining Raycast/release best-practice updates without merging the PR:\n\n- Added semantic release tag validation in the CLI release workflow (expects vX.Y.Z-style tags).\n- Added post-upload release asset listing for workflow visibility.\n- Hardened checksum parsing in install.sh.\n- Checked Raycast author configuration. ReScience Lab is not accepted by Raycast as an author handle (lint returns 404 and rejects spaces), so I set the valid account handle to Yilin for now. To publish under ReScience Lab, create/claim a Raycast account or team handle without spaces, then we can update author.\n\nRevalidated:\n- tests/install.sh\n- cargo test --manifest-path cli/Cargo.toml\n- cd raycast-extension && npm run lint\n- cd raycast-extension && npm run build

[Jing-yilin]

Double-checked Devin's latest findings and fixed the actionable issues:\n\n- Added Clap-powered perch --version.\n- Installer now verifies the downloaded binary identifies as Perch via --version before installing.\n- Tightened release tag validation to exact vX.Y.Z.\n- Made release asset upload failure explicit with a clear error/exit.\n- Updated installer tests for binary identity validation.\n\nRevalidated:\n- cli/target/debug/perch --version\n- cargo test --manifest-path cli/Cargo.toml\n- tests/install.sh\n- cd raycast-extension && npm run lint && npm run build\n\nRemaining note: Devin suggested GPG/cosign signature verification. I did not add that because it requires choosing/managing a signing strategy/key or GitHub artifact attestations. The installer already verifies SHA-256 checksums before execution, but repo/release compromise protection should be handled as a separate release-hardening decision.