feat: apply suggestions via API (auto-fix remote)

[brucearctor]

Context

Programmatic auto-fix by applying code suggestions through the platform API.

• GitLab: PUT /suggestions/:id/apply / PUT /suggestions/batch_apply
• GitHub: GraphQL only (not available via REST API)

E9 Concerns

This requires a different workflow: post suggestion → get suggestion ID from response → apply. It also modifies the source branch, which has safety implications.

Recommend implementing as a separate --auto-fix-remote flag in a future PR. Need dogfooding data first.

Safety

• Must not modify source branch without explicit opt-in
• Should require suggestion to be posted first (not inline edit)
• Batch apply for efficiency on GitLab

Ref

E9 design session in conversation 8ecd8c13