feat(tools): add letter length + summary depth controls; harden korrespond §-discipline

- Summarize: new depth param (brief/standard/detailed) with depth-aware prompt
  instructions and coverage mandate; wired through API + JS
- Korrespond: new letter length param (concise/standard/detailed) injected as
  Lengde: instruction in draft pass; wired through API + JS
- Korrespond draft prompt: add §-discipline rule (cite only directly relevant §§)
  plus Opphevet guard (aligned with dobetterlegal-tools)

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

assets/js/korrespond.js

@@ -281,6 +281,7 @@
       force_draft:    !!forceDraft,
       use_my_case:    (typeof window.dbnGetUseMyCase === 'function') ? window.dbnGetUseMyCase() : false,
       engine:         (document.querySelector('[name="korrEngine"]:checked')?.value ?? 'azure_mini'),
+      length:         (document.querySelector('[name="korrLength"]:checked')?.value ?? 'standard'),
     };
     if (korrDocIds.length) payload.doc_ids = korrDocIds;
     if (persona) payload.profile = persona;