ci: name the plugin jobs for product groups

[LKSNDRTMLKV]

The plugins are product group plugins (plugins/product-group-*), but CI still called them sector plugins.

Changes

• ci.yml: the job Sector plugin tests becomes Product group plugin tests. Its three steps are renamed the same way.
• wasm-build.yml: the job sector-plugins / WASM build — sector plugins becomes product-group-plugins / WASM build — product group plugins.
• docs/regulatory/CONFORMITY.md: the one prose mention.

The comment in wasm-build.yml that describes the old plugins/sector-* directory names is left as is. It records history.

🚨 Merge order: the ruleset names this check

Sector plugin tests is a required status check in the main ruleset. This PR's CI reports Product group plugin tests instead, so the ruleset keeps it blocked until the required check is renamed. Changing it is a repository setting, so it is done by hand:

1. Land whatever is open under the old name first.
2. In Settings → Rules → Rulesets → main → Require status checks to pass, replace Sector plugin tests with Product group plugin tests.
3. Merge this PR.
4. Other open PRs report the new name once they merge main, which the up-to-date rule makes them do anyway.

WASM build — product group plugins is not a required check, so its rename needs nothing else.

Context

The Sector plugin tests job was cancelled twice on 2026-10-05, once on main and once on a PR, each time after exactly 15 minutes. The annotation said "The job was not acquired by Runner of type hosted even after multiple attempts". That was GitHub runner capacity, not the job's code, and re-runs were requested. This PR only renames the job.