Docs/apify webhook example (#177)

* docs: add end-to-end Apify webhook example

Captures the exact flow validated against real Apify infrastructure on
2026-04-21: two buttons (scrape launcher + dataset fetcher) + one
drawer with webhook trigger. Real trip time: ~15s from press to
`[serve] drawer on-apify-done ok`.

Exercises the whole webhook surface in one walk-through:
  - batteries for the Apify token (globally scoped, stays out of repos)
  - `buttons webhook setup` with the cert.pem flow, apex guard, and
    zone-drift detection
  - alternative --api-token path for multi-zone / headless
  - `${inputs.webhook.body.resource.defaultDatasetId}` CEL resolution
  - auto-declared `webhook` input on trigger drawers
  - drawer-level retry policy on transient upstream 502s
  - listener drain + process-group kill on Ctrl-C
  - dry-run via `press --webhook-body` without running the listener

Flags a known gap: `drawer NAME set on_failure.*` is not yet wired;
direct JSON edit of drawer.json is the current path. Worth a follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: move examples/ to repo root

Promotes the examples folder out of docs/ to the repo root so it's
discoverable alongside README/CLAUDE.md without spelunking into the
Mintlify docs tree. Both walk-throughs move:

- examples/apify-to-snowflake.md       (drawer composition reference)
- examples/apify-webhook-scrape.md     (just-added webhook reference)

Updates the single CLAUDE.md reference to the new paths.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bobakemamian