feat(settings): add QMD memory preset controls

[slicenferqin]

Linked Issues

• Closes QMD 记忆系统 #249

Summary

• Add a dedicated QMD Memory card in Settings.
• Add one-click QMD low-token preset action via config.get + config.patch.
• Add one-click fallback action to switch memory backend back to builtin.
• Add runtime memory probe action via doctor.memory.status.
• Add full i18n coverage for zh/en/ja.

Why

Issue #249 asks whether ClawX supports QMD memory and highlights high token usage. This PR delivers a practical first-step UX for enabling QMD and applying conservative context controls directly from GUI.

What this preset writes

• memory.backend = "qmd"
• memory.qmd.* basic update/session/limits defaults
• agents.defaults.contextPruning.*
• agents.defaults.compaction.* (including memoryFlush)

Validation

• pnpm run lint
• pnpm run typecheck
• pnpm run test

Notes

• This PR focuses on a safe, operator-friendly first version.
• Per-agent granularity and richer QMD knobs can be added in a follow-up PR.