* fix: add MaxTokens and Temperature fields to AgentInstance and update related logic
* feat: add MaxTokens and Temperature options to SubagentManager and update tool loop logic
* feat: add default temperature handling and update related tests
* feat: allow temperature 0 and distinguish unset
* fix: format MockLLMProvider struct in subagent_tool_test.go
Resolve conflicts in pkg/providers/types.go and pkg/agent/loop.go:
- types.go: use protocoltypes aliases from PR #213, keep fallback types
- loop.go: drop old single-agent createToolRegistry (replaced by multi-agent pattern)
Refactor to align with PR #213 patterns:
- instance.go: use NewExecToolWithConfig (accept full config for deny patterns)
- registry.go: pass full config to NewAgentInstance
- loop.go: add Perplexity web search options to registerSharedTools