Tighten skill guidance and split command reference

[haymovie]

Summary\n- slim down SKILL.md to keep only the triggering guidance and operating rules\n- remove nonstandard extra frontmatter and over-broad replacement claims\n- add a small reference file for curated command examples instead of embedding a giant command catalog\n\n## Why\nThe current skill works conceptually, but the raw packaging is heavier than it needs to be for an agent skill. This keeps the trigger description strong while reducing context bloat and making the skill easier to follow. It also adds guardrails around prerequisites, write-action confirmation, and fallback to browser automation when opencli-rs is not the right fit.\n\n## Notes\n- kept the core value proposition intact: use opencli-rs for supported authenticated browser/app sessions\n- intentionally did not try to duplicate the full upstream CLI docs inside SKILL.md; the CLI repo and --help already cover that well\n- tested locally on Windows: binary install succeeded, opencli-rs --help worked, public-mode hackernews top worked, and doctor correctly reported missing browser daemon/extension state when Chrome was not connected\n