Remove deprecated UI settings extension (adk-ts, adk-ui)

[PetrBulanek]

Feature Description

The legacy UI settings extension (ui/settings/v1) was deprecated in favor of the form
extension with settings_form demand (services/form/v1). The Python SDK side was already
cleaned up (#118), but the TypeScript SDK and UI still contained legacy code.

Proposed Solution

adk-ts

• Delete src/client/a2a/extensions/ui/settings/ module (index, types, schemas)
• Remove ui/settings re-exports from barrel files (extensions/index.ts, types.ts, schemas.ts)
• Remove settings extension extractor, fulfiller, and demand resolution from handle-agent-card.ts
• Remove deprecated settings property from Fulfillments type in core/extensions/types.ts

adk-ui

• Remove transformLegacySettingsDemandsToSettingsForm() and transformSettingsFormValuesToLegacySettingsValues() from settings/utils.ts
• Simplify AgentDemandsProvider.tsx: settings form now reads directly from form extension demands instead of falling back to legacy settings demands
• Simplify build-fulfillments.ts: remove legacy settings fulfillment block and related params

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Additional Context

No response