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>

korrespond.php

@@ -70,6 +70,15 @@ require_once __DIR__ . '/includes/layout.php';
                         <label><input type="radio" name="korrTone" value="warm"> Conciliatory-warm</label>
                     </div>
 
+                    <!-- Letter length -->
+                    <div class="control-row" id="korrLengthControl">
+                        <span class="control-label">Letter length</span>
+                        <label><input type="radio" name="korrLength" value="concise"> Concise</label>
+                        <label><input type="radio" name="korrLength" value="standard" checked> Standard &#9733;</label>
+                        <label><input type="radio" name="korrLength" value="detailed"> Detailed</label>
+                    </div>
+                    <p class="upload-hint">Concise: short and to-the-point (2-3 paragraphs). Standard: balanced correspondence. Detailed: full background, all arguments, and complete legal reasoning.</p>
+
                     <!-- Engine -->
                     <div class="control-row" id="korrEngineControl">
                         <span class="control-label">Engine</span>