Release v0.4.0 installer with shared web and CLI account

[TeoSlayer]

Installer v0.4.0 connects agents, the web app, and an installed Cosift CLI to the same account. After verifying the MCP connection, it hands the existing token to the CLI through the subprocess environment; the CLI validates it and saves a private, origin-bound session. Subsequent CLI requests work without copying credentials from harness configuration.

The release defaults directly to the production Cloud Run auth/MCP origins, so installation works independently of custom-domain DNS. It includes pinned v0.2.7 binary download instructions that verify SHA-256 and minisign before installation, using the published Cosift public key.

Existing sessions are never overwritten. --cli requires a compatible installed CLI and successful handoff; --no-cli skips it. An absent CLI leaves automatic agent installation usable. Documentation covers same-email web login and the shared-token consequences of logout/account switching.

Validation:

• make check: generated/embedded onboarding payload, POSIX shell syntax, ShellCheck, and all 255 onboarding checks passed.
• Installer handoff suite: all 11 cases passed, including installer → real CLI login → 0600 session → separate CLI credits request with no credential or server flags.
• Default production endpoints are covered without making live auth requests.
• Full reachable Git history and all GitHub issue/PR/release content scanned with Gitleaks: zero findings. Custom ck-token scan found only deterministic test fixtures.

Depends on the CLI support merged in pilot-protocol/cosift#58 and signed v0.2.7 release assets. Publishing the v0.4.0 and v1 installer tags and enabling production Cloud Run invocation are coordinated release steps.