[Fix] Cost totals drop when users delete tasks

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Keep persisted inference usage in Cost Analytics after its linked task is soft-deleted.
• Replace deleted-task titles, user attribution, task links, and task type details with a privacy-safe Deleted task attribution.
• Continue excluding deleted tasks from pull request attribution while preserving active-task behavior.
• Add a database regression covering historical cost and token totals plus deleted-task privacy boundaries.

Why this change was made

Soft-deleting task history previously removed its persisted usage from aggregate reporting, causing historical provider spend and token totals to change even though the underlying charge remained real.

Impact

Cost Analytics now remains an accurate historical ledger when tasks are deleted. Deleted tasks still contribute to task counts and averages, but their private task details and navigation are not exposed.

[roomote-community]

No code issues found. See task

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