fix(critique): validate tokenBudget and costBudgetUsd in TokenBudgetBreaker (#3666)

[djm204]

Fixes #3666.

Description

TokenBudgetBreaker compared spend.totalTokens against config.tokenBudget without validating numeric sanity. If tokenBudget was undefined, NaN, or non-positive, comparisons failed or evaluated unpredictably.

Changes

• TokenBudgetBreaker.check() validates config.tokenBudget and throws a ConfigurationError if !Number.isFinite(tokenBudget) or tokenBudget <= 0.
• Validates config.costBudgetUsd (if specified) to ensure it is a non-negative number (>= 0).
• Added comprehensive unit tests covering missing/NaN/negative configuration edge cases in token-budget.test.ts.

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[djm204]

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[djm204]

Closing as superseded. Main already has this PR's tokenBudget validation (merged via #3896, identical logic/message). This PR's costBudgetUsd check also has the same bug that #3843 was filed against — it uses Number.isNaN(costBudgetUsd) instead of Number.isFinite(costBudgetUsd), so it still doesn't reject Infinity. #3843 is fixed properly (using Number.isFinite) in #3886, currently open and mergeable. No remaining unique content here; closing rather than asking for a rebase.