Usage → Pricing tab is read-only: no UI to add/edit/reset custom pricing overrides

[liuxiaocs7]

Problem

The Usage statistics surface has a Pricing tab (定价配置) that is display-only. The Runtime Host side of pricing overrides is fully built — pricing.query / pricing.mutate (upsert + delete) in HostUsagePricingCoordinator, PricingStore in @maka/storage, and the usage:pricing:list / usage:pricing:put / usage:pricing:reset IPC handlers in the Desktop main process — but none of it is reachable from the UI:

• The preload bridge never exposes the pricing mutation channels, so the renderer cannot call them.
• UsagePricingPanel only renders a table of existing custom overrides; it has no add / edit / reset affordance.

So the tab always shows "No pricing overrides", and a user cannot register a custom price for a model whose built-in pricing is missing or wrong — that model's cost then reads as unavailable in the summary.

Desired outcome

From the Pricing tab I can:

• add a custom per-model price (provider + model, input/output rate, optional cache read/write rates);
• edit an existing override;
• reset (remove) an override so the model falls back to the built-in pricing table.

Alternatives or workarounds

None from the UI today — the only way to populate an override is to drive the IPC/store directly, which isn't user-accessible.

[liuxiaocs7]

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