Remove Enable AI header toggle

[wprashed]

What?

Closes #600

Removes the Enable AI header toggle from the AI settings page (routes/ai-home/stage.tsx), cleans up remaining globalEnabled UI disabling logic, and allows individual feature and experiment group toggles to directly control plugin functionality.

Why?

The Enable AI header toggle displayed a binary ON/OFF state that did not accurately reflect individual feature configurations. Per maintainer consensus in #600, this PR removes the global header toggle entirely, allowing individual feature toggles and category group toggles (or deactivating the plugin / using core filters) to manage functionality.

How?

• Removed the Enable AI header <ToggleControl> and InfoTip from routes/ai-home/stage.tsx.
• Removed unused globalToggleDescription, GLOBAL_FIELD_ID, noop, and DisabledToggle component from stage.tsx.
• Removed globalEnabled prop and conditions from SectionActions and VisualCardToggle in stage.tsx, ensuring individual toggles and bulk action buttons remain interactive.
• Removed .ai-showcase-card--disabled CSS rule from routes/ai-home/style.scss.
• Updated is_globally_enabled() in includes/Abstracts/Abstract_Feature.php to default to true when option is not explicitly set.
• Updated Playwright E2E helpers (tests/e2e/utils/helpers.ts) in disableExperiments and enableExperiments to wait for section action buttons to render before counting, correctly capture settings save responses, and toggle showcase cards.
• Updated tests/e2e/specs/admin/settings.spec.js to assert section button states and removed the obsolete test for disabled global bulk actions.

Use of AI Tools

AI assistance: Yes
Tool(s): Antigravity
Model(s): Gemini 2.5 Pro
Used for: Diagnosing E2E test failures, updating settings UI components and E2E test assertions, and structuring the PR according to repository guidelines.

Testing Instructions

1. Go to the AI settings page (options-general.php?page=ai-wp-admin).
2. Confirm the header renders cleanly with Docs, Contribute, and options links, without the Enable AI header toggle.
3. Confirm section group toggles ("Enable all" / "Disable all") and individual feature toggles are enabled and continue to work as expected.
4. Verify that running npm run typecheck, npm run lint:js, and npm run build pass without errors.

Screenshots or screencast

Before	After
Header includes "Enable AI" toggle	Header has no "Enable AI" toggle; features are managed via section buttons and toggles

Changelog Entry

Removed - The Enable AI header toggle from the AI settings page.

[github-actions]

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Unlinked Accounts

The following contributors have not linked their GitHub and WordPress.org accounts: @manueldiaz2006t-blip.

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Unlinked contributors: manueldiaz2006t-blip.

Co-authored-by: wprashed <wprashed@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>
Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
Co-authored-by: andreilupu <euthelup@git.wordpress.org>
Co-authored-by: JasonTheAdams <jason_the_adams@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.55%. Comparing base (a7657e1) to head (41cbb0e).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #985   +/-   ##
==========================================
  Coverage      75.55%   75.55%           
  Complexity      3381     3381           
==========================================
  Files            138      138           
  Lines          13081    13081           
==========================================
  Hits            9883     9883           
  Misses          3198     3198           

Flag	Coverage Δ
unit	75.55% <100.00%> (ø)

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[dkotter]

E2E tests are failing here.

In addition, please ensure the PR description contains everything from our PR template, as already mentioned here