[Feature]: Pass thinking level to Claude Code provider as effort parameter

[FrankThonig6]

Summary

Forward thinking level from GSD2 to the Claude Agent SDK's effort parameter when using the claude-code provider.

Problem to solve

• The GSD2 thinking level is not taken into account for the claude-code provider's effort level
• Claude Code uses its own default or the value from .claude/settings.json independently

Current behavior

• streamViaClaudeCode in stream-adapter.ts receives options.reasoning but does not read it
• buildSdkOptions() does not accept or forward an effort parameter
• The Anthropic provider (anthropic.ts) correctly maps options.reasoning to effort via mapThinkingLevelToEffort() and guards with supportsAdaptiveThinking() — both from anthropic-shared.ts

Expected behavior

• The claude-code provider should forward thinking level as effort, matching the Anthropic provider's pattern
• When thinking is "off", reasoning is undefined and effort should be omitted, allowing .claude/settings.json effortLevel to take effect as the default

Implementation note

The required helpers (mapThinkingLevelToEffort, supportsAdaptiveThinking) exist in anthropic-shared.ts but are not accessible to the claude-code extension — @gsd/pi-ai does not export them via the barrel or a subpath.

Use cases

• User selects thinking level in GSD2 UI → agent loop passes options.reasoning to provider → claude-code provider forwards as effort to Agent SDK → Claude Code applies effort level

Impact

• Affected: all users of the claude-code provider
• Frequency: every claude-code session
• Consequence: thinking level UI control is non-functional for claude-code provider