Release 0.5.0 without self-update

[konojunya]

Summary

• Ship the already implemented doctor, read-only config discovery, and versioned JSON output in CLI 0.5.0.
• Remove the self-update command, executable replacement code, and dedicated dependencies; document Homebrew/Aqua-owned updates and verified manual downloads.
• Introduce distribution contract v2 without updater ownership or activation. Preserve the original schemas and immutable release history.
• Separate current source and published release versions so release preparation continues to test the existing verified Aqua artifacts.
• Regenerate shell completions and the offline manual and add removed-command regression coverage.

Validation

• Rust unit, command, render, formatter and template conformance tests passed.
• Clippy passed with warnings denied.
• 59 repository contract/workflow/schema tests and 12 packaging tests passed.
• Generated shell/manual assets are exact; full CI and release artifact verification remain required before publication.

The existing 0.4.0 installation pins stay in place until the 0.5.0 artifacts have been published and verified. No Cargo or self-update channel is activated by this change.