feat: auto-seed common config snippets from live files on first setup…(首次初始化时自动从配置文件填充通用配置片段)

[jiawei666]

… (Claude + Codex + Gemini)

Mirrors the desktop cc-switch initialize_common_config_snippets flow:

• On first startup with empty common config, extract shared settings from live config files (permissions, statusLine, hooks, non-auth env, Codex shared TOML tables, Gemini proxy env) into common_config_ snippets.
• Non-destructive: default provider retains full original settings.
• Gate: skipped if snippet already exists or was explicitly cleared.
• OpenCode/Hermes/OpenClaw excluded: their common config merge mechanism is a no-op, and extractors don't match the shape of read_live_settings for additive-mode apps.