fix: improve core stability and optional MCP websocket dependency handling

[wul48527-code]

Background

This PR addresses several stability issues found during local usage:

• MCP optional websocket dependency errors appearing during startup.
• Core execution-path regressions around iteration propagation, registry path caching, workflow ID collisions, and UI summary rendering.
• Missing regression tests for these behaviors.

Changes

• MCP optional dependency handling:
  • Graceful degradation when websockets is missing.
  • Clear import-time guidance only when websocket transport is actually used.
• Core stability fixes:
  • Ensure resolved max_iterations is passed in no-skill execution path.
  • Reuse dedicated skill-selection LLM client instead of recreating it repeatedly.
  • Normalize and validate auto-registered skill dirs before caching.
  • Avoid workflow summary ID collisions for duplicate leaf dir names across different roots.
  • Fix f-string syntax in UI summary output.

Tests

Added/updated regression tests:

• tests/test_tool_layer.py
• tests/test_mcp_server.py
• tests/test_dashboard_server.py
• tests/test_mcp_connectors_optional.py

Local validation:

• py -3.13 -m unittest discover -s tests -v
• Result: all tests passed.

Compatibility

The changes are backward compatible and primarily improve robustness and error handling.

[wul48527-code]

补充测试说明（便于 review）：

• 本地环境：Windows + Python 3.13
• 执行命令：
  py -3.13 -m unittest discover -s tests -v
• 结果：全部通过（本 PR 分支 6/6）

本 PR 关注点：

• MCP websocket 可选依赖缺失时的优雅降级
• 执行路径与目录注册稳定性修复
• workflow 汇总 ID 冲突修复
• UI summary f-string 语法修复

如有需要，我可以把任意一个修复点再拆成更小 commit 方便逐个审阅。

[Dennis-yxchen]

Thanks for the thorough investigation. We've reviewed each item and cherry-picked the two changes that address real bugs into main:

• max_iterations not forwarded in no-skill execution path — merged in 2fb8024 with regression tests
• Workflow ID collision across roots — merged in the same commit, reworked to use a hash-based ID scheme instead of __-joined paths (the __ separator was ambiguous when directory names also contain __)

You're credited as co-author on both fixes.

Changes we're not including:

• WebSocket graceful degradation — a missing optional dependency should fail loudly at the point of use, not silently swap in a stub class. Users need to know they need to pip install websockets, not discover it later.
• LLMClient reuse in _get_skill_selection_llm — premature optimization; the client is lightweight and the current behavior is correct.
• _normalize_skill_dir path caching — the existing behavior works; adding normalization introduces complexity without a demonstrated bug.
• f-string syntax fix — Python 3.12+ (PEP 701) allows nested quotes in f-strings, so this is not a bug on supported versions.