fix(agent): stream thinking for all adaptive Claude models, not just Opus 4.7

Extended thinking was gated on a hardcoded `model === "claude-opus-4-7"` check,
so newer/other adaptive models (Opus 4.8, Opus/Sonnet 4.6) fell into the classic
`thinking: { type: "enabled" }` branch. Adaptive models default thinking display
to "omitted", so no thinking was streamed — the UI showed nothing for Claude while
DeepSeek (a separate openai-compatible path) worked.

Replace the string check with a pure helper `anthropicThinkingProviderOptions`
that mirrors opencode's transform.ts detection:
  - adaptive (`type: "adaptive"`) for Opus 4.7+ (version-parsed) and Opus/Sonnet
    4.6 (id substring; handles dash and dot forms);
  - `display: "summarized"` ONLY for Opus 4.7+ (they default to omitted and must
    be forced); Opus/Sonnet 4.6 stream thinking without it;
  - all other Claude models keep classic `enabled` + budgetTokens.

Pure function (no provider/streamText/network), unit-tested directly: Opus 4.8
(the reported bug), Opus 4.7, Sonnet/Opus 4.6, Opus 4.5 + dated Sonnet (enabled),
a future Opus 4.9 (proves version-parse), and effort->budget mapping.

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