fix: align docs with current CLI

[fullstackjam]

What does this PR do?

Align the CLI and contributor docs with the current implementation, and replace the removed openboot delete guidance in the config-limit error with the dashboard URL.

Why?

The README and changelog incorrectly said doctor and update were removed, AGENTS.md still described the deleted install screen and progress-event flow, and HARNESS.md contradicted the existing fmtprint architecture rule.

Testing

• go vet ./... passes
• Relevant tests added or updated
• Tested locally (./openboot install --dry-run or similar) — not applicable to documentation and error-message changes
• go test ./internal/cli/... ./internal/archtest/...

Cross-repo checklist

• No docs/content update is needed in openboot.dev
• No CLI ↔ server API contract change

Notes for reviewer

The config-limit regression test now verifies that the dashboard is suggested and the removed openboot delete command is not.