feat: AI bulk generate button + progress modal on product list (P0 #2)

[roboshyim]

What

Adds an "AI bulk generate" button to the product list smart-bar (next to Add product) that opens a confirmation modal and kicks off the background bulk-description job from P0 #2.

How it works

• Overrides the sw_product_list_smart_bar_actions_add block in sw-product-list (the inner block, not the outer ..._actions block) — this avoids re-declaring the <template #smart-bar-actions> named slot, which caused a Vue render crash (reading 'type').
• Button is disabled until ≥1 product row is selected; label shows the selected count.
• Modal lets the merchant pick tone and max words, shows N products selected, then POSTs to the bulk endpoint and lets the merchant close the window while the job runs in the background.

Verification (browser, live admin on 6.7.2.2)

• ✅ Button renders in smart bar, disabled with no selection
• ✅ Enables after selecting products (shows count)
• ✅ Modal opens with form (tone=Professional, max words=180, Cancel + Start generation)
• ✅ Start generation → no Vue crash, no duplicate-slot error, job row created in frosh_ai_bulk_job and processed by the message handler
• ✅ No render exceptions in console (only pre-existing $t deprecation warnings)

End-to-end pipeline confirmed: button → modal → API → frosh_ai_bulk_job insert → messenger dispatch → provider call. (The only runtime failure in dev is HTTP 401 from a dummy API key — expected without a real provider key.)

Notes

• The dev container needed bin/console database:migrate FroshAI --all to create frosh_ai_bulk_job — an environment gap, not a code change.

[roboshyim]

LGTM — verified locally. The fix to override the inner sw_product_list_smart_bar_actions_add block (instead of re-opening the #smart-bar-actions slot) is correct: re-opening that named slot alongside {% parent %} creates a duplicate slot definition and crashes Vue slot render in sw-product-list. Applied the diff on top of main and ran the PHPUnit suite in the dev container: 116 tests, 461 assertions, OK. No PHP changes, so no new backend tests needed. Merging.