fix(ai): collect trailing local tool approvals

[iroiro147]

Summary

• Collect local tool approval responses from the latest assistant approval turn even when user or system context follows the approval response.
• Skip approvals that already have tool results and avoid replaying approvals behind a later assistant response.
• Align missing-result validation with the same latest-assistant approval boundary.

Fixes #17033

Tests

• pnpm --filter ai test:node -- collect-tool-approvals.test.ts stream-text.test.ts convert-to-language-model-prompt.validation.test.ts
• pnpm --filter ai test:edge -- collect-tool-approvals.test.ts stream-text.test.ts convert-to-language-model-prompt.validation.test.ts
• pnpm --filter ai type-check
• pnpm exec oxfmt --check packages/ai/src/util/get-latest-assistant-approval-turn.ts packages/ai/src/generate-text/collect-tool-approvals.ts packages/ai/src/generate-text/collect-tool-approvals.test.ts packages/ai/src/generate-text/stream-text.test.ts packages/ai/src/prompt/convert-to-language-model-prompt.ts packages/ai/src/prompt/convert-to-language-model-prompt.validation.test.ts
• pnpm exec oxlint packages/ai/src/util/get-latest-assistant-approval-turn.ts packages/ai/src/generate-text/collect-tool-approvals.ts packages/ai/src/generate-text/collect-tool-approvals.test.ts packages/ai/src/generate-text/stream-text.test.ts packages/ai/src/prompt/convert-to-language-model-prompt.ts packages/ai/src/prompt/convert-to-language-model-prompt.validation.test.ts