feat: add Claude Code agent provider

[signet-bot-codex]

Summary

• add a new ClaudeProvider agent provider using ai-sdk-provider-claude-code@3.4.4
• add a ClaudeToolsAdapter to expose TENEX tools as an SDK MCP server for Claude Code
• register the new claude provider across provider ids, registry exports, usage metadata extraction, and agent-provider initialization paths
• update minimal config UX so Claude Code is treated as a no-key provider with a sonnet default model
• add focused provider and adapter tests

Verification

• bun test src/llm/providers/__tests__/providers.test.ts src/llm/providers/agent/__tests__/ClaudeProvider.test.ts src/llm/providers/agent/__tests__/ClaudeToolsAdapter.test.ts ✅
• bun run typecheck ✅
• bun run lint ❌ repo-wide pre-existing failures outside this change set
• bun run lint:architecture ❌ repo-wide pre-existing architecture/cycle failures outside this change set

Notes

• ClaudeProvider is implemented fresh against current master and the current CodexProvider shape, using old Claude-provider history only as reference for Claude-specific integration details.
• I also updated my local ~/.tenex/llms.json to add a claude config and switch the default to it for Athena testing, but that local runtime config change is not part of this PR.