fix(anthropic): default adaptive thinking display to summarized

[Sayt-0]

Summary

Effort levels set via /effort or the Shift+Tab thinking cycle showed no reasoning in the TUI on newer Claude models (Opus 4.7+, Fable 5). Those models omit thinking content server-side by default, and docker-agent only sent the adaptive display field when provider_opts.thinking_display was configured.

/effort | Shift+Tab
  -> runtime override: ThinkingBudget{Effort: ...}
  -> anthropic: thinking.type=adaptive + output_config.effort
  -> display field only sent when thinking_display is configured
  -> server default on Opus 4.7+/Fable 5 = omitted
  -> only the signature is returned, no thinking blocks, TUI shows nothing

Fix

Request summarized thinking whenever adaptive/effort-based thinking is used without an explicit thinking_display, on both the GA and Beta request paths. thinking_display: omitted remains the explicit opt-out.

Case	Before	After
Adaptive/effort, no thinking_display, Opus 4.7+/Fable 5	no display sent, API defaults to omitted, reasoning hidden	display=summarized, reasoning visible
Adaptive/effort, no thinking_display, Opus 4.6/Sonnet 4.6	no display sent, API defaults to summarized	display=summarized, unchanged behavior
Explicit thinking_display	honored	honored
Token-count budgets	no display sent	unchanged (API already defaults to summarized)

Changes

• pkg/model/provider/anthropic/thinking.go: defaultAdaptiveDisplay applied in applyThinkingConfig and applyBetaThinkingConfig
• pkg/model/provider/anthropic/thinking_test.go: adaptive cases now expect summarized; new Fable 5 cases (default summarized, explicit omitted preserved)
• Docs: Thinking Display sections updated (docs/guides/thinking, docs/providers/anthropic, docs/configuration/models)

Validation

• go build ./..., go test ./pkg/model/... ./pkg/modelinfo/... ./pkg/runtime/... ./pkg/effort/...: pass
• golangci-lint run and go run ./lint .: 0 issues
• Docs YAML snippets validated by TestDocYAMLSnippetsAreValid

Notes

• The Bedrock provider also sends thinking.type=adaptive without a display field; if the same gap applies there, it can be addressed in a follow-up.
• A model-gated alternative (a modelinfo.HidesThinkingByDefault predicate) was considered; the unconditional default was preferred because it is a no-op for models whose server default is already summarized and automatically covers future models that hide thinking by default.