Make token and cost reporting transparent and model-aware

[raphant]

Problem

The interface presents one token total and an approximate dollar value.
Users cannot tell which counts came from runtime usage data, which counts were estimated, or which model price produced the dollar value.

Proposed change

Track the source and category of each token count.
Show the model, pricing basis, and estimation status beside every cost total.

Acceptance criteria

• Counts distinguish reported values from estimates.
• The cost view identifies the model and price table entry used.
• Input, output, cached, reasoning, and tool-result tokens remain separate when the runtime reports them.
• Unknown models do not silently use an unrelated price.
• Tests cover known, unknown, estimated, and runtime-reported usage.

Source

• web/components/agent-visualizer/canvas/draw-cost.ts calculates and draws current costs.
• extension/src/token-estimator.ts estimates tokens when exact usage is unavailable.