[Dev] Implement integration-ready blocks and app placeholders

[hta218]

Context

Most production merchants need 3rd-party apps. Maison should provide integration-ready surfaces without hard-coding every possible vendor.

Goal

Implement integration-ready blocks/placeholders for the most common app categories, using safe fallback states and clear configuration patterns.

Scope

Implement selected integration-ready surfaces based on approved design:

• Reviews summary/stars/review carousel placeholder
• Wishlist button/state placeholder
• Back-in-stock form placement
• Subscription selector placement if relevant
• Klaviyo/newsletter signup section
• Size guide integration point
• Loyalty points hint if relevant
• Analytics/pixel-safe extension points if required

Technical requirements:

• Avoid exposing private/admin tokens in browser code
• Use public env vars only for client-safe keys
• Keep vendor-specific logic isolated
• Add safe empty/unconfigured fallback states
• Add README/docs notes or link to docs issue for setup details

Blocked by

• [Design] Design advanced sections and integration-ready blocks
• Theme/global integration docs decisions if they affect implementation

Acceptance criteria

• Integration surfaces are implemented with safe fallback states.
• Public/private env boundaries are respected.
• Vendor-specific code is isolated and documented.
• Blocks are usable/configurable through Weaverse where appropriate.
• Build/typecheck/lint pass.
• Setup notes are linked or included.

Verification

Run build/typecheck/lint and verify both configured and unconfigured states where possible.

Metadata

• Theme: Maison
• Track: Theme Refresh
• Priority: High
• Milestone: July-2026