Move domain-specific SEO, media, and email abilities out of core

[chubes4]

Problem

Data Machine core still directly loads and registers several vertical product/domain ability sets.

Code references on origin/main (008878b6):

• data-machine.php:187-192 — requires media and SEO ability files.
• data-machine.php:209 — requires email ability file.
• data-machine.php:282-287 — instantiates media and SEO abilities.
• data-machine.php:321-330 — instantiates email fetch/publish abilities.

Examples:

• SEO: inc/Abilities/SEO/*, inc/Abilities/InternalLinkingAbilities.php.
• Media: inc/Abilities/Media/*.
• Email: inc/Abilities/Email/EmailAbilities.php, inc/Abilities/Fetch/FetchEmailAbility.php, inc/Abilities/Publish/SendEmailAbility.php, inc/Abilities/Publish/SendEmailQueuedAbility.php.

There is already precedent for moving feature abilities out: GitHubAbilities moved to data-machine-code extension in data-machine.php.

Why this matters

Core 1.0 should be the orchestration/runtime substrate: agents, jobs, flows, steps, files, handler registration, generic WordPress/content primitives, permissions, and APIs. SEO, media generation/rendering, and email client behavior are valuable features, but they read as extension-plugin domains rather than core substrate.

Acceptance criteria

• Decide the 1.0 core boundary for domain abilities.
• Move SEO/media/email ability registration to one or more extension plugins, or document why each belongs in core.
• Keep any generic primitives needed by extensions in core with narrow interfaces.
• Preserve migration/activation behavior for existing installs that use these abilities.
• Tests or smoke checks confirm core still boots without the extracted feature plugins.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: 1.0 technical-debt audit and issue drafting; Chris requested tracking issues for the findings.