UI: Standardize button sizing to 40px across all experiments

[i-anubhav-anand]

What?

Closes #701

Add the __next40pxDefaultSize prop to all Button components that were missing it, and enforce it going forward via an ESLint rule.

Why?

Several action buttons across the plugin were rendering at the deprecated 36px height while others were already at 40px, creating visible inconsistency. The Gutenberg component standard has designated 40px as the default and retired 36px (gutenberg#46734, gutenberg#46741).

How?

• Added __next40pxDefaultSize to all primary/secondary/tertiary text Button components that were missing it across 13 component files:
  • src/experiments/content-resizing/components/ContentResizingToolbar.tsx
  • src/experiments/meta-description/components/MetaDescriptionPanel.tsx
  • src/experiments/meta-description/components/MetaDescriptionModal.tsx
  • src/experiments/editorial-updates/components/EditorialUpdatesPlugin.tsx
  • src/experiments/excerpt-generation/components/ExcerptGeneration.tsx
  • src/experiments/alt-text-generation/components/AltTextControls.tsx
  • src/experiments/alt-text-generation/components/MediaEditorAltTextControl.tsx
  • src/experiments/connector-approval/components/PendingRequestsCard.tsx
  • src/admin/ai-request-logs/components/SettingsPanel.tsx
  • src/features/image-generation/components/GenerateImageStandalone.tsx
  • src/features/image-generation/components/GenerateImageInlineModal.tsx
  • src/features/image-generation/components/MediaLibraryImageEditor.tsx
  • src/features/image-generation/components/shared/index.tsx
• Icon-only buttons, size="compact", size="small", variant="link", and ToolbarButton instances are intentionally excluded per upstream convention.
• Added '@wordpress/components-no-missing-40px-size-prop': 'error' to eslint.config.mjs to prevent regression.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): claude-sonnet-4-6
Used for: Implementation assistance; code reviewed and verified by me.

Testing Instructions

1. Open a post in the editor.
2. Check the Meta Description sidebar panel — "Generate Meta Description" should now render at 40px height.
3. Check the "Apply Editorial Updates" button in the post status panel — same height as neighbouring buttons.
4. Trigger the Alt Text generation controls on an image block — Apply/Dismiss/Generate buttons all 40px.
5. Open the image generation feature — all action buttons (Save, Refine, Generate Another, Edit Prompt, Cancel) at 40px.
6. Run npm run lint:js — should pass with no new violations.

Screenshots or screencast

Before	After
Buttons inconsistently 36px / 40px	All primary/secondary/tertiary buttons 40px

Changelog Entry

Fixed - UI: standardized button sizing to 40px across all experiments and features (Content Resizing, Meta Description, Editorial Updates, Excerpt Generation, Alt Text, Connector Approval, Request Logs, Image Generation). Added ESLint rule to prevent regression.

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[dkotter]

This PR is based against trunk which is not correct (should be develop). It also duplicates work already done in #702. Please don't open new PRs to solve an issue that already has a PR.