feat(cli): rename diagnose to doctor (keep deprecated alias until 0.3.0)

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Summary

Renames the environment health-check command from diagnose to doctor, following the established CLI convention (flutter doctor, brew doctor, expo doctor). diagnose stays as a deprecated alias, so this is non-breaking and can ship in 0.2.x; the alias is scheduled for removal at 0.3.0 (recorded in the PRD).

Changes

• CLI: command renamed to doctor; diagnose kept as an alias (command.Aliases). --help shows diagnose, doctor.
• Internal types (ubiquitous-language consistency): DiagnoseQuery / DiagnoseQueryHandler / DiagnoseError / DiagnoseCommand → Doctor* (files renamed via git mv). DiagnosticCheck / DiagnosticStatus are unchanged — the doctor runs diagnostic checks.
• Docs: PRD (EN/JP) command tree + §6.4 updated, with the alias deprecation and its 0.3.0 removal target stated; README (EN/JP) subcommand map; ADR 0003 control-plane mention.

Tests (TDD)

New DoctorCommandTests (written Red-first, 3 cases): command is named doctor; diagnose is registered as an alias; parsing diagnose resolves to the doctor command. Full suite green (692 tests).

Verification

• ivicli doctor and ivicli diagnose both run the health checks on the real binary.
• No remaining diagnose references in code or docs except the deprecation notes and an unrelated English verb in ADR 0017.