fix(openai-compat): retain complete calls

[calclavia]

Preserve complete tool calls when an OpenAI-compatible stream reaches the output limit.

buffered arguments -> secure JSON parser
                        |
                        +-- valid ------------> tool-call
                        +-- invalid + length -> omit call
                        +-- invalid + normal -> existing error

finish reason + usage -> preserved

.changeset/complete-tools-on-length.md              +5/-0
packages/ai/openai-compat/
  src/OpenAiLanguageModel.ts                       +10/-8
  test/OpenAiLanguageModel.test.ts                +183/-0
packages/ai/clavia/test/ProviderStreams.test.ts      +7/-1

Rebased onto clavia/ai-providers at bb7b490; unrelated publishing history removed. OpenRouter's separate adapter remains outside this fix.

Validation: 88 targeted tests pass; pnpm lint-fix and pnpm check pass.