feat: add Legal Translation tool (translate.php)

New dedicated tool for translating Norwegian legal documents (Barnevernet
letters, court decisions, correspondence) into the user's chosen language
with legal-terminology annotations.

- translate.php: new tool page with source/target language selectors,
  4-way UI lang switcher, file upload, doc picker, streaming results
- api/translate.php: NDJSON streaming endpoint; Azure GPT-4o-mini with
  legal-aware prompt that preserves Norwegian statute refs verbatim and
  annotates terms with no target-language equivalent; 2-credit cost
- assets/js/translate.js: form handler, NDJSON stream reader, copy button
- assets/css/tools.css: .lt-* styles for translation result + annotations
- includes/i18n.php: 22 lt_* keys × 4 languages; translate entry in nav
- includes/FreeTier.php: translate → 2 credits
- includes/CaseResults.php + case-result.php: translate in eligible tools,
  toolLabel, toolIcon, deriveTitle, rendering block, rerun map

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

includes/CaseResults.php

@@ -34,6 +34,7 @@ final class CaseResults
         'redact',
         'transcribe',
         'legal-analysis',
+        'translate',
     ];
 
     /** True when the user is on a tier that gets saved results (Plus, Pro, or active Plus trial). */
@@ -240,6 +241,7 @@ final class CaseResults
             'redact'         => 'Anonymisering',
             'transcribe'     => 'Transkripsjon',
             'legal-analysis' => 'Juridisk analyse',
+            'translate'      => 'Oversettelse',
         ][$tool] ?? ucfirst($tool);
     }
 
@@ -258,6 +260,7 @@ final class CaseResults
             'redact'         => '🖊️',
             'transcribe'     => '🎙️',
             'legal-analysis' => '⚖️🇳🇴',
+            'translate'      => '🌐',
         ][$tool] ?? '📄';
     }
 
@@ -276,6 +279,7 @@ final class CaseResults
             'redact'        => [$input['text'] ?? null],
             'transcribe'    => [$input['filename'] ?? null],
             'legal-analysis' => [$input['doc_type'] ?? null, $input['text'] ?? null],
+            'translate'      => [$input['source_lang'] ?? null, $input['target_lang'] ?? null, $input['text'] ?? null],
             default         => [$input['title'] ?? null, $input['query'] ?? null, $input['text'] ?? null],
         };
         foreach ($candidates as $c) {