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/summarize.js

@@ -186,6 +186,7 @@
             text:     combined,
             language: _currentLang,
             engine:   engine,
+            depth:    (document.querySelector('input[name="sumDepth"]:checked') || {}).value || 'standard',
             slices:   slices,
         };
         if (docIds.length) payload.doc_ids = docIds;