Integrate dbn-legal-agent-v2: upgrade all v1 refs + add Korrespond legal-check

- Replace dbn-legal-agent with dbn-legal-agent-v2 in bootstrap.php
  (dbnToolsRunLegalCheck), DeepResearchAgent.php (interpretSeed,
  expandQueries, synthesis fallback, deploy label), BvjAnalyzerAgent.php
  (check_model label) — 8 locations total
- Add dbn-legal-agent-v2 legal threshold check to KorrespondAgent:
  called after selfCheck() in both generate() and refine(); result
  surfaced as legal_check[] in the API response
- Render legal_check card in korrespond.js using existing bvj-red-flag
  styles; shows only when non-empty
- Add .korr-legal-check CSS block in tools.css

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

includes/BvjAnalyzerAgent.php

@@ -968,7 +968,7 @@ PROMPT;
                 foreach ($checkFindings as $cf) {
                     $json['procedural_red_flags'][] = $cf;
                 }
-                $json['check_model'] = 'dbn-legal-agent';
+                $json['check_model'] = 'dbn-legal-agent-v2';
             }
         }