api: expose match_mode/match_score in CLI/MCP JSON replace results

[SebTardif]

Context

EditResult.match_mode / match_score (#1662) are library fields only. CLI --json and MCP replace tools do not surface them, so agents using those surfaces still cannot warn on low-confidence fuzzy matches.

Acceptance

• JSON envelopes for replace (CLI + MCP + tx change summary where applicable) include match_mode and optional match_score
• Serde snake_case values match library enum (exact / fuzzy / anchored)
• Tests lock the JSON fields

Related

Library fields landed in #1667; honesty gap for non-library hosts.