feat: begin WPistic platform + LTD entitlement integration

[Shubochandrosarker]

Phase 1: non-breaking WPistic platform integration

This starts the Insightistic-first rollout into the shared WPistic commercial control plane.

Included

• Adds Insightistic_Platform_Bridge as a compatibility layer between the existing Insightistic connector/license flow and the shared WPistic\Sdk\Licensing entitlement authority.
• Preserves all existing free Insightistic functionality and existing api.insightistic.com customer connections.
• Treats active/grace-period WPistic licenses as valid for new paid/LTD capabilities.
• Exposes safe boolean/numeric entitlement helpers for sites, AI credits, client workspaces, white-label and agency features.
• Adds regression coverage for legacy-only, WPistic-active, grace-period and revoked-license states.

Intentionally not included yet

• Bundling/booting the shared WPistic WordPress SDK.
• Marketplace/AppSumo redemption UI.
• Moving Insightistic cloud data ingestion off the existing connector.

Those are follow-up phases after compatibility tests are green.

Related platform branch: feature/insightistic-product-rollout.