refactor(cli): use fixMarkdown for fix mode

[luojiyin1987]

completed by #112

Parent

• refactor(core): replace positional lintMarkdown arguments with an options-based lint and fix API lint-md#188

What to build

Use Core fixMarkdown for CLI fix mode after lint-md/lint-md#229 is stable.

Keep lint mode on the legacy lint-only call. Keep the current worker protocol unchanged.

Acceptance criteria

• Fix mode calls fixMarkdown.
• Lint mode keeps its current legacy Core call.
• The worker keeps the current isFixMode field.
• Rule settings reach both Core calls unchanged.
• Existing lint output stays unchanged.
• Existing --fix output stays unchanged.
• Existing fix metrics stay available in development output.
• Existing convergence warnings stay unchanged.
• Existing unapplied-fix warnings stay unchanged.
• Worker tests cover lint and fix modes.

Blocked by

• feat(core): add an explicit fixMarkdown API lint-md#229

Non-goals

• A new lint-only Core API.
• Worker protocol changes.
• Metrics configuration.
• Core legacy API deprecation.