Route Claude executor through llm-providers

[stackbilt-admin]

Summary

• routes executeClaudeChat and executeClaudeChatStream through @stackbilt/llm-providers instead of direct Anthropic fetch/SSE parsing
• preserves the existing AEGIS tool loop for in-process tools and MCP tools using provider-native toolCalls / toolResults
• forwards edgeEnv through Claude and GPT-OSS tool execution so dynamic tools can execute under provider-backed paths
• adds focused regression coverage for Claude provider tool rounds and streaming callback behavior

Refs #24. This completes the Anthropic/D.1 executor migration slice; the broader epic should remain open for legacy composite/scheduled/raw provider cleanup.

Validation

• npm run typecheck
• npx vitest run tests/claude-provider.test.ts tests/executors.test.ts
• npm test
• npx charter validate
• git -c core.whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol diff --check
• npm pack --dry-run