docs(variables): retire the dev Variables pages, redirect to help (PRDCT-554)

[Iamfle4ka]

What & why

Second half of the two-PR shape for the Variables unit (PRDCT-583). The content is already migrated to help — this retires the dev-side originals so there is exactly one maintained copy.

Old dev URL	New home
/integrate/variables/	https://help.keboola.com/components/variables/api/
/integrate/variables/tutorial/	https://help.keboola.com/components/variables/api/tutorial/

Placement and naming are owner-decided, not proposed here:

• Components as the home — Jordan, 08-05 sync: flows are technically a component, as are transformations.
• "Variables", not "Variables API" — Matyáš, 08-07 in #ask-component-factory: "Call it Variables and I don't mind wherever it is. Components as a page is fine." There is no separate Variables API product — the calls are configuration/Storage API plus Vault.

What changed

• Both pages become redirect_to stubs — the same shape as the already-merged /integrate/mcp/ retirement (docs(mcp): retire the dev MCP page, redirect to help (PRDCT-580) #405).
• Four assets deleted (countries.csv, variables.svg, two tutorial screenshots); the help pages carry their own copies, verified in dist.
• Both entries dropped from the Integrate nav.

Deliberately not in this PR

• _layouts/redirect.html — the friendly "this page has moved" template lands with docs(extend): retire the merged component docs, redirect to help (PRDCT-543) #406. Until then jekyll-redirect-from uses its own template, so the redirect works either way; no need to add the same file in two open PRs.
• extend/component/index.md:94, the only inbound link from outside this subtree, is left pointing at /integrate/variables/ — it redirects, and docs(extend): retire the merged component docs, redirect to help (PRDCT-543) #406 turns that whole file into a stub anyway. Repointing it here would only conflict with docs(extend): retire the merged component docs, redirect to help (PRDCT-543) #406.

Merge order

Draft on purpose: this must not merge before connection-docs#1051, which publishes the target pages. #1051 is green and mergeable, waiting on review.

🤖 Generated with Claude Code

[linear-code]

PRDCT-554

[keboola-pr-reviewer-bot]

Verdict: needs_human (risk 3/5) · profile docs

Escalating: nav-data edit, two page retirements, and asset deletions all trip always-needs-human rules.

Impact flags: possible rollback re-introduction — see Check Run summary.

Concerns:

• _data/navigation.yml: Navigation data changed; drives site-wide sidebar rendering — always requires human review.
• integrate/variables/index.md: Live page gutted to redirect stub; page retirement can break inbound links.
• integrate/variables/countries.csv: Four assets deleted; remaining references unverifiable (code search unavailable).
• + 1 more concern — see Check Run summary.

Suggested reviewers: @keboola/docs

[davidesner]

LGTM