Jira init, doctor, adoption rehearsal, and public documentation

[jeffhuber]

Part of #797. Depends on the functional Jira issues.

Problem

The feature is not adoptable unless init, upgrade, doctor, docs, and a disposable rehearsal describe the same safe path.

Outcome

Ship Jira setup and upgrade ergonomics suitable for an experienced engineer adopting Code Mower cold.

Scope

• Add init prompts/flags and generated configuration without changing existing generated workflow names.
• Add tagged setup, credential, mapping, dry-run, apply, troubleshooting, and rollback documentation.
• Add doctor --adoption checks for tracker configuration, auth, project/issue type, JQL, permissions, transitions, rate limits, and write guards.
• Add an offline first-user rehearsal and a live read-only checklist.
• Add an owner-authorized disposable write-test checklist, disabled by default.
• Scrub examples for personal, tenant, project, host, and filesystem identifiers.

Acceptance Criteria

• GitHub-only quickstart remains the default and does not mention Jira until the optional integrations step.
• One concise Jira guide takes an adopter from token/profile to read-only controller preview.
• Existing-repo setup drift is reviewable and non-destructive.
• Public docs are accurate, consistent, metadata-only, and use placeholders.

CODE_MOWER_BUILDER:antigravity