chore: update deps, dependabot and bump version

[justlevine]

What

Rolls back several artificicial deps and bumps others to their latest compatible versions. Triggers a version bump too.

Why

Prerelease cleanup

Related Issue(s):

How

Testing Instructions

Screenshots

Additional Info

Checklist

• I have read the Contribution Guidelines.
• I have read the Development Guidelines.
• My code is tested to the best of my abilities.
• My code passes all lints (ESLint etc.).
• My code has detailed inline documentation.
• I have updated the project documentation as needed.
• I have added a changeset for this PR using npm run changeset.

[Copilot]

Pull request overview

This PR prepares a new 1.1.0 release by aligning metadata/docs with the current codebase and adjusting dependency management to more sustainable, compatible versions.

Changes:

• Bumps the plugin version to 1.1.0 across plugin headers, constants, and readme metadata, and introduces a dedicated CHANGELOG.md.
• Updates Composer, npm, and WordPress-related dependencies (including PHPStan/PHPUnit and @wordpress/* packages), rolling back one dev plugin to an earlier compatible version.
• Refines Dependabot configuration to group and schedule Composer, npm, and GitHub Actions updates on a weekly cadence instead of daily/multi-ecosystem defaults.

Reviewed changes

Copilot reviewed 8 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
readme.txt	Updated minimum WordPress version and stable tag, removed inline changelog/requirements, and added a link to an external changelog (with a couple of inconsistencies noted in comments).
package.json	Adjusted WordPress JS, linting, and build-related dependencies to newer (or compatible) versions while keeping React versions stable.
onemedia.php	Synced the plugin header and ONEMEDIA_VERSION constant to the new 1.1.0 release version.
docs/INSTALLATION.md	Updated installation system requirements to WordPress ≥ 6.8 and PHP ≥ 8.0 to match the plugin header.
composer.lock	Regenerated lockfile to reflect updated PHP tooling versions (PHPStan, PHPUnit, Sebastian libs) and the rollback of wpackagist-plugin/plugin-check to 1.6.0.
composer.json	Pinned wpackagist-plugin/plugin-check to the ~1.6.0 series to match the rolled-back version in the lockfile.
README.md	Removed the inline changelog section to centralize change history in the new CHANGELOG.md.
CHANGELOG.md	Added a new changelog file documenting releases 1.1.0, 1.0.1-beta, and 1.0.0-beta.
.github/dependabot.yml	Replaced broad, frequent updates for many ecosystems with a more focused schedule and grouped updates for Composer, npm, and GitHub Actions (with one group-overlap issue noted).

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