feat: agentic commerce settings page

[David Neustadt (dneustadt)]

Agentic Commerce settings page integration

Implements the plugin side of the Agentic Commerce settings page. The Core ships a static settings page with extension points (shopware/shopware#21250); this PR makes it live once the plugin is active.

• relates #20945

What this does

Admin — overrides the Core sw-settings-agentic-commerce page (only when it exists, so 6.5/6.6 are unaffected):

• Marks the "extension installed" step complete and drives the readiness counts, step completion, subtitle, and shop-readiness status from the plugin.
• Adds the Prepare sales channels flow: a modal with a sales-channel multi-select listing the unprepared Storefront/Headless channels (all pre-selected), which activates UCP + the AI files for the selected channels and refreshes the page state. Gated on ucp.editor with a tooltip when the privilege is missing.

API / services:

• GET /api/_admin/ucp/readiness — returns prepared, agentic, and transactional sales-channel counts (ReadinessSummaryProvider).
  • prepared = Storefront/Headless channels with UCP active; agentic = agentic-commerce type channels.
• POST /api/_admin/ucp/prepare — prepares the given channels (SalesChannelPreparationService → UcpConfigService::activate(), which enables UCP with the default capabilities plus the AI files). Only transactional channels are prepared; others are skipped. Gated on ucp.editor.

How to test

1. Install/activate the plugin on a shop running the Core page from feat: agentic commerce settings page shopware#21250.
2. Open Settings → Commerce → Agentic Commerce: the first step shows as complete and the counts reflect the shop.
3. Click Prepare sales channels, confirm the selection in the modal, and verify the prepared count increases and the step/headline move to the ready state once all eligible channels are prepared.
4. As a user without ucp.editor, verify the prepare button is disabled with an explaining tooltip.