fix(desktop): Usage Statistics activity log always shows "未命名会话" in the 任务 (Task) column

[liuxiaocs7]

What happened

On the Usage Statistics page (使用统计) → Activity records (活动记录), the 任务 (Task) column shows 未命名会话 · <short id> ("Untitled session · …") for every row — even when the underlying session has a real title in the WorkHub.

Expected: named sessions show their real title in the Task column; only genuinely untitled sessions fall back to 未命名会话 · <id>.

This is a regression. #3833 fixed exactly this column by carrying the session name (SessionHeader.name) through the old packages/storage/src/usage-stats-store.ts pipeline. That pipeline was later replaced by the Runtime Host usage projection (#3697), and the old store was deleted (#4060). The new pipeline only carries sessionId, never the session name, so UsageRequestLog.sessionName is declared but never populated — and the UI's usageSessionDisplayLabel always hits the untitled fallback for every row.

How to reproduce

1. Open Settings → Usage Statistics (使用统计).
2. Have some model/tool activity in sessions that carry real titles.
3. Open the Activity records (活动记录) tab and look at the 任务 (Task) column.
4. Every row reads 未命名会话 · <short id>, regardless of whether the session actually has a name.

Environment

• Maka commit: aa586237e
• OS and version: macOS (Darwin 24.6.0)
• Surface: Desktop
• Node.js version: running from source

Logs, screenshots, or additional context

Root cause — sessionName is dropped at every layer of the current usage pipeline:

• packages/core/src/settings.ts — UsageRequestLog.sessionName is declared (with a doc comment) but no producer fills it.
• apps/desktop/src/main/runtime-host-usage-ipc-main.ts — projectLlmLog / projectToolLog carry sessionId/turnId but never sessionName.
• packages/runtime-host/src/protocol/usage-pricing.ts — the projection types (LlmUsageLogProjection / ToolUsageLogProjection) have no session-name field at all.
• The UI already reads row.sessionName (apps/desktop/src/renderer/settings/usage-settings-page.tsx, usageSessionDisplayLabel), so no UI change is needed — the data layer just needs to populate the field again.

Raw usage rows (UsageLogRow) are keyed only by sessionId; the human-readable title lives in the session catalog. Recovering the name is a sessionId → name join, which the deleted store used to do.

[liuxiaocs7]

take