fix(anthropic): honor custom apiModelId instead of silently defaulting to claude-sonnet-4-5

[grizmin]

Summary

• AnthropicHandler.getModel() coerced any apiModelId not present in the static anthropicModels table down to anthropicDefaultModelId ("claude-sonnet-4-5") — and that coerced id is what actually got sent as model in the API request, silently ignoring a user-configured custom model name.
• The same fallback broke capability lookups used to build the thinking request param: an unrecognized id inherited the default model's (older) capability profile, so custom deployments of newer models (e.g. Sonnet 5 class) got the legacy thinking: {type: "enabled", budget_tokens} shape instead of {type: "adaptive"}, which those models reject with a 400.
• Fix: the model id sent to the API always honors a user-configured apiModelId. For unrecognized values, capabilities are best-effort guessed via known model-family substring matching (same pattern as the existing BedrockHandler.guessModelInfoFromId).

Fixes #418
Fixes #843

Test plan

• Added regression tests in anthropic.spec.ts covering: custom model id preserved in getModel().id, capability guessing via substring match, fallback to default info when no family matches, and createMessage sending the raw custom id with thinking: {type: "adaptive"}.
• pnpm --filter zoo-code test - 50/50 passing
• pnpm --filter zoo-code check-types - clean
• pnpm --filter zoo-code lint - clean

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