docs(bdd): scenarios for paste-a-URL + onboarding burst, mapped to tests

Adds paste_url.feature (valid/invalid/not-found/dedup, +@pending no-captions)
and an onboarding-burst scenario on connect; all non-pending scenarios mapped in
the coverage gate to their existing Go tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/use-cases/connect_account.feature

@@ -24,6 +24,12 @@ Feature: Connect and manage video accounts
     Then a discovery pass for my account is triggered right away
     And I do not have to wait for the next scheduled pass to see my videos
 
+  Scenario: Connecting summarizes my newest videos right away
+    Given I have no connected video accounts
+    When I connect my YouTube account
+    Then up to the onboarding cap of my newest videos are summarized through the rate gate
+    And the rest are left to the scheduled recency-bounded pass
+
   Scenario: Tokens are never stored in the clear
     When I connect any video account
     Then no OAuth token value is stored in the database