fix: preserve effective config and parse init options without weakening settings

[chtnnh]

Problem

init starts from built-in defaults instead of the effective home configuration, and absent CLI options are treated as explicit false values. A plain re-init can disable an existing requireTrailer setting; --require-trailer true is also parsed incorrectly.

Scope

Use effective configuration as the initialization baseline and make option parsing tri-state and strictly typed.

Acceptance criteria

• Home defaults survive first repo initialization unless explicitly overridden.
• Re-running init preserves omitted boolean settings.
• --require-trailer true and false behave as documented.
• Invalid boolean values fail rather than silently selecting a value.
• Tests cover home/repo precedence and repeated initialization.