Use mwfl 0.2.1 structured diagnostics

[everettjf]

What changed

• link the pinned mwfl 0.2.1 diagnostics component
• format Liney's local log records through mwfl's structured diagnostic event envelope
• retain Liney's existing timestamp, bounded rotation, crash recovery and privacy-conscious ZIP policy
• verify the exported diagnostic bundle contains the structured event and excludes sensitive history/dump content

Why

This is a low-risk second mwfl adoption boundary. mwfl now owns stable event formatting, PID/TID attribution, UTF-8 conversion and pre-sink sanitization, while Liney keeps its application-specific recovery and export behavior.

This PR intentionally does not replace Liney's crash-dump writer yet. Liney uses MiniDumpWithThreadInfo; mwfl 0.2.1 does not expose that policy. The companion mwfl PR adds it without forcing Liney to downgrade dump quality.

Validation

• git diff --check
• GitHub CI passed: Ubuntu unit tests, Windows 2022 full build/smoke/stress, and Windows 2025 full build/smoke/stress
• recovery self-test verifies the mwfl event envelope is exported while command history, secrets and minidump memory remain excluded

Stack

• base: agent/use-mwfl-0.2.1-deployment / PR Use mwfl 0.2.1 for deployment verification #10
• companion mwfl API improvement: Add privacy-conscious thread-info minidumps mwfl/mwfl#5