Fix HOME volume mount, genericize topic, add progress statuses, extract lexicon

- Volume was mounted at ~/.claude only, but claude-code writes auth to
  ~/.claude.json too — that file lived on the ephemeral container layer and
  was lost on every recreate. Now the whole $HOME is on the named volume,
  and claude-config moved outside HOME (/app) so it isn't shadowed by it.
- Default /news topic was hardcoded to AI; now it's a configurable
  DEFAULT_TOPIC (plain "главные новости дня"), topic is fully free-form.
- Prompt now instructs Claude to send interim "⏳ ..." progress updates via
  send_to_telegram while researching, not just the final digest — a bare
  request like "call this tool" was already taking 3+ minutes end-to-end,
  so silence read as broken.
- All user-facing/prompt text moved into bot/lib/lexicon.dart.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bot/lib/claude_runner.dart

@@ -3,6 +3,7 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'config.dart';
+import 'lexicon.dart';
 
 enum ClaudeOutcome { success, busy, timeout, failure }
 
@@ -73,16 +74,11 @@ class ClaudeRunner {
   }
 
   String _buildPrompt({required int chatId, String? topic}) {
-    final base = topic == null || topic.isEmpty
-        ? config.newsPrompt
-        : 'Проведи ресёрч последних новостей и трендов по теме "$topic" за последние '
-            '7 дней. Используй поиск в интернете. Составь краткую выжимку: 5-8 пунктов, '
-            'у каждого — суть в 1-2 предложениях и ссылка на источник.';
-
-    return '$base\n\n'
-        'Когда выжимка готова, ОБЯЗАТЕЛЬНО вызови инструмент send_to_telegram с '
-        'параметрами chat_id=$chatId и text=<готовый текст в Markdown, с заголовком>. '
-        'Это единственный способ доставить материал — не выводи финальный ответ никак '
-        'иначе, только через вызов этого инструмента.';
+    final effectiveTopic = (topic == null || topic.isEmpty) ? config.defaultTopic : topic;
+    return [
+      Lexicon.researchInstruction(effectiveTopic),
+      Lexicon.progressInstruction(chatId),
+      Lexicon.finalDeliveryInstruction(chatId),
+    ].join('\n\n');
   }
 }