fix(models): keep claude-4-sonnet-thinking in the Sonnet 4 family

[avs-io]

Problem

Cursor's unversioned claude-4-sonnet-thinking slug was aliased to claude-sonnet-4-5, even though it identifies the thinking variant of Sonnet 4.

This is easy to miss today because Sonnet 4 and Sonnet 4.5 currently have identical rates. The incorrect identity nevertheless surfaces the wrong model name and could become a pricing error if those rates diverge.

Change

• map claude-4-sonnet-thinking to claude-sonnet-4
• update the Cursor alias regression table
• add an independent display-name assertion that pins the model identity even while the two models share pricing

User impact

Cursor sessions using this slug now appear under Sonnet 4 rather than Sonnet 4.5 and remain attached to the correct pricing family.

Validation

• npx vitest run tests/models.test.ts — 154 passed
• npm test — 2,617 passed, 5 skipped
• npm run test:locks — 26 passed
• npx tsc --noEmit
• npm run build:cli
• npm --prefix dash run build
• runtime probe resolves the slug to Sonnet 4

Addresses the confirmed model-alias finding in #912.