Move the checks onto the shared umbrella and build the other dev branch weekly [ignore_release]

[snake14]

Description

Separate commits so any part can be reverted on its own.

The pull request checks move behind the shared umbrella. The workflows this replaces were already thin callers of the same shared workflows, so what changes is that one caller invokes them rather than several — a check added centrally now reaches this plugin without a pull request here. It also drops the concurrency group the AI checklist workflow carried, which spans both of the umbrella's lanes and silently defeats them.

Opted out where the check does not apply here: skip-phpstan. Each carries its reason inline.

A LICENSE file is added (GPL v3+), copied verbatim from sibling plugins declaring the same licence — this plugin shipped none, so the license check had nothing to check.

Verified live on matomo-org/plugin-LogViewer and innocraft/plugin-UsersFlow: a manual dispatch resolved the default branch, dispatched the build on the other one, and that build completed green attributed to that branch — which is what the plugin build dashboard's per-branch badges read.

Issue No

No GitHub issue.

Steps to Replicate the Issue

1. Note that the matomo-tests.yml cron only ever fires on the default branch.
2. Expected result: the other maintained dev branch is built weekly too.
3. Actual result: it has had no scheduled build since the default branch changed.

Checklist

• [✔] Tested locally or on demo2/demo3?
• [NA] New test case added/updated?
• [NA] Are all newly added texts included via translation?
• [NA] Are text sanitized properly? (Eg use of v-text v/s v-html for vue)
• [NA] Version bumped?
• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules
• [NA] Documentation updated?