fix: hide history cost estimates for subscription-billed tasks (#13562)

* fix(vscode): hide history cost estimates for subscription-billed tasks

The task-header fix for subscription providers cannot reach history:
history rows render the stored totalCost (an API-rate estimate) and do
not know which provider ran the task, so the history page printed
$X.XXXX on every row and the recent-task chips in an empty chat view
rendered a $ chip even for subscription-billed tasks.

The SDK session records already persist the provider — the CLI's
history view uses it for exactly this — but the VS Code mappers dropped
it. Map it through both transports (HistoryItem.apiProvider for the
state-pushed taskHistory, TaskItem.api_provider for getTaskHistory) and
suppress the dollar figure per row when that provider's
usageCostDisplay is not "show", via a new useUsageCostVisibility
predicate shared by both surfaces.

Rows without a recorded provider (tasks predating the field, legacy
imports) keep showing the stored value — there is nothing to key
suppression on.

* test(vscode): e2e-verify history cost suppression in real VS Code

Seeds SDK session records (one openai-codex subscription task, one
anthropic usage-billed task) into the isolated CLINE_DIR before the
webview loads, then asserts in a real VS Code instance that both the
recent-task chips and the full history page render the dollar figure
only for the usage-billed task. Covers the two boundaries the unit
tests stub: on-disk records reaching getTaskHistory with provider
populated, and the provider listings delivering the subscription mark
to the webview.