Add shell-discovery guidance and example skeletons to the zapier-sdk skill

[BenMcGit]

Summary

• New "Shell discovery" section in SKILL.md. Agents doing discovery from a shell were reinventing basic flows because the skill front-loaded the SDK library and pushed CLI content into references/cli.md. zapier-sdk --help doesn't advertise --json (it's a per-command flag), so agents kept parsing the default table output. The new section shows the four essential commands and the canonical find-first-connection --json | jq -r '.data.id' -> run-action chain, and clarifies that default output is best for reading; --json is for piping.
• Rewrote the app-key gotcha. The old wording implied the CLIAPI-suffixed form (NotionCLIAPI) was universal. In practice, only the SDK library's sdk.runAction({ appKey }) requires it; the CLI's run-action, findFirstConnection, listActions, and so on all accept the short slug too.
• New multi-connection gotcha. Users often have several connections per app (personal + work Gmail, multiple Slack workspaces). Default to findFirstConnection and take the first result rather than stopping to disambiguate.
• New references/examples.md. Fill-in-the-blank skeletons for a plain single-action script, a Zapier Tables script, and a durable notify-on-event workflow. Every placeholder is called out (<app-slug>, <AppCLIAPI>, <action-key>, ...). Opens and closes with pointers back to the verified corpus at examples/ and https://github.com/zapier/sdk/tree/main/examples so agents don't ship the unverified skeletons themselves.

Test plan

• Skim the new Shell discovery section and confirm the CONN=$(...) -> run-action snippet works against a fresh login.
• Confirm the rewritten app-key gotcha reads unambiguously as SDK-library-only.
• Skim references/examples.md: every placeholder is obviously a placeholder, and the "real corpus lives here" pointers land at the start and end of the file.
• Existing CI (validate.yml) still green (no changes to gated paths).