[4/4] docs: generate API reference samples that run, in current idioms

[dazzatronus]

Run against a local server, no POST sample in the reference worked in any language. Most sent no body, Ruby, Java and HTTP never sent the API key, Go didn't compile, and NodeJS needed node-fetch, which no longer supports require.

This replaces widdershins's sample templates with templates/code-samples. Each template reads like the sample it produces; the shared logic (header selection and rendering JSON as each language's literals) lives in sample.def. Every sample reads the key from SHOTSTACK_API_KEY (HTTP shows YOUR_API_KEY) and uses the language's current client: built-in fetch, requests, Guzzle 7, Ruby's Net::HTTP, java.net.http and Go's net/http. Optional headers are left out, so the Generate samples no longer all send one fixed Idempotency-Key.

tests/reference-code-samples.cjs runs all 176 samples, plus each language against a body built to break string quoting, and checks the method, path, key and body that arrive. CI installs the eight runtimes.

Also fixes the Direct Upload samples, which called the Edit API: the build-docs.sh rewrite missed /upload.

463 lines: the templates and the check that proves them land together, because the check fails on the old templates.

Verify: CI step "Check reference code samples" → 184 of 184 ran correctly.

Stack (merge in order)

	PR	Adds	Why it is separate
1/4	#147 (merged)	Keeps <?php in rendered PHP samples	A Shins fix, independent of what the samples contain
2/4	#151 (merged, released as 1.20.2)	Current, valid examples in the spec	Changes the published spec, so it releases a patch
3/4	#148 (merged)	Shows each request body's example in the reference	Docs build only
4/4 ← this PR	#149	Current-idiom sample templates and a check that runs them	Depends on the examples; the check and templates land together

[github-actions]

🎉 This PR is included in version 1.20.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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