Add agent-ready mode to basectl repo init

[codeforester]

Goal

Add an opt-in basectl repo init mode that creates a Base-managed repository ready for issue-backed human or AI-agent implementation work on GitHub.

Background

Base already separates the local repository baseline from optional agent guidance through basectl repo agent-guidance. That keeps ordinary repo bootstrap conservative, but it also makes the agent-ready path a second manual step. As Base moves toward a GitHub-centered agentic coding platform, new repositories should have an explicit one-command path that seeds the repo baseline plus agent-facing guidance and GitHub workflow files.

Scope

• Add an opt-in flag such as --agent-ready to basectl repo init.
• In agent-ready mode, create the normal Base baseline and the maintained agent guidance files for repositories that do not already have them.
• Decide whether .github/copilot-instructions.md, .github/ISSUE_TEMPLATE/implementation.yml, and .github/workflows/copilot-setup-steps.yml belong in the first generated set or should be split into follow-up issues.
• Preserve the existing repo agent-guidance command for existing repositories.
• Update README, docs/repo-baseline.md, command reference, completions, and AI context if the public command surface changes.

Acceptance Criteria

• basectl repo init <name> --agent-ready --dry-run prints the files and GitHub steps it would add without writing them.
• Non-dry-run agent-ready mode creates the normal baseline plus approved agent-ready files without overwriting existing files.
• repo init without --agent-ready keeps current behavior.
• repo init --agent-ready --pr stages only the generated files and opens the same style of draft PR as existing generated-file flows.
• Focused BATS coverage proves dry-run, non-overwrite, PR, and help/completion behavior.

Validation

• Relevant cli/bash/commands/basectl/tests/repo.bats tests.
• Relevant repo-agent-guidance or generated-file BATS tests if split coverage exists.
• Help/completion docs tests touched by the new flag.
• git diff --check.

Non-Goals

• Do not make agent guidance the default for every repo init.
• Do not require GitHub Copilot, Codex, Claude, or any provider-specific agent.
• Do not add secrets, tokens, personal editor settings, or local Codex configuration.
• Do not replace the existing repo agent-guidance command.

Project Fields

• Priority: P2
• Status: Backlog
• Size: M
• Area: CLI
• Initiative: Adoption Polish

Agent Assignment

Copilot candidate after triage. The issue should be implementable once the exact generated-file set is confirmed.