[Feature Request] Add optional session running cost indicator for subscription users

Description
Optional "running cost" indicator for subscription users

Problem summary:
Subscription users can't see real-time cost,
which will hurt if pricing model evolves to use-based costs, as with the API model.

Details:
Today, API users see per-call cost as a billing line item. Subscription
users see effort metrics (/context token counts) but no dollar translation.
The users who'd most benefit from cost-awareness — subscription users
who'll need to adjust habits if/when pricing models change — are the ones
not shown it.

Concrete request:
Optional opt-in "session running cost" indicator,
either as a small status-bar number ("~$X.XX so far") or expandable side
panel. Not enabled by default; users opt in via Settings.

Why opt-in?

• Avoids cost-anxiety friction for users who'd rather not see it.
• Lets engagement-focused users keep current "all you can eat" feel.
• Builds cost-awareness muscle memory for users who want it, before

any pricing-model transition makes it suddenly relevant.

Same translation logic the API billing already uses; the data is already
computed (token counts shown in /context). Mostly a UI surface, not new
infrastructure.

Pair-programming use case: when iterating on doc edits or formatting in
chat, a visible cost ticker would naturally encourage tighter prompts
and shorter back-and-forth. Today the same iteration burns context
silently. Visibility = self-discipline without paywall coercion.

Environment Info

• Platform: linux
• Terminal: vscode
• Version: 2.1.123
• Feedback ID: d6ad30b7-23dc-4a5a-b8c2-1a59e7efede5

Errors

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