feat: complete Sprint 2 with Telegram notifications integration

Add Telegram Bot notification node to n8n workflow:

New Features:
- Telegram notification node for critical severity logs
- Italian message template with emoji and MarkdownV2 formatting
- Smart routing: Telegram only for critical logs
- Error handling: continueOnFail prevents workflow interruption
- Environment-based configuration (TELEGRAM_CHAT_ID)

Message Template Includes:
- 🚨 Alert header with severity
- 📍 Server hostname identification
- 📝 AI-generated problem summary
- 💡 Suggested bash command in code block
- ⚠️ Confirmation required flag
- 📝 Additional notes from AI
- 📊 AI processing status
- 🤖 Model used (openai/gpt-4o-mini)
- ⏰ Localized Italian timestamp

Workflow Flow:
Webhook → HMAC → Validation → PostgreSQL → OpenRouter → Critical? → Telegram → Response
                                                      ↓ FALSE
                                               Success Response

Configuration Required:
1. Create Telegram Bot via @BotFather
2. Get TELEGRAM_BOT_TOKEN
3. Get TELEGRAM_CHAT_ID via @userinfobot
4. Configure credentials in n8n UI
5. Set TELEGRAM_CHAT_ID environment variable

Documentation:
- docs/telegram_setup.md: Setup instructions
- .env.example: Environment variables template
- .gitignore: Protect sensitive telegram_setup.md
- docs/prd.md: Updated Sprint 2 completion status

Sprint 2 Complete:
✅ Secure log ingestion (bash)
✅ n8n webhook workflow
✅ OpenRouter AI integration
✅ PostgreSQL storage
✅ HMAC authentication
✅ Telegram notifications

Refs: docs/specs/ai_pipeline.md, docs/specs/bash_ingestion_secure.md

workflows/logwhisperer_ingest.json

@@ -140,6 +140,31 @@
         100
       ]
     },
+    {
+      "parameters": {
+        "chatId": "={{ process.env.TELEGRAM_CHAT_ID }}",
+        "text": "={{ '🚨 *LogWhisperer Alert* \\n\\n📍 *Server:* ' + $json.hostname + '\\n⚠️ *Severity:* ' + $json.severity.toUpperCase() + '\\n\\n📝 *Problema:*\\n' + $json.ai_analysis.sintesi + '\\n\\n💡 *Comando suggerito:*\\n```bash\\n' + ($json.ai_analysis.comando || 'Nessun comando disponibile') + '\\n```\\n\\n⚠️ *Richiede conferma:* ' + ($json.ai_analysis.richiede_conferma ? 'SÌ' : 'NO') + '\\n📝 *Note:* ' + ($json.ai_analysis.note || 'Nessuna nota') + '\\n\\n📊 *Analisi AI:* ' + $json.ai_status + '\\n🤖 *Modello:* ' + ($json.ai_model || 'N/A') + '\\n\\n⏰ ' + new Date().toLocaleString('it-IT') }}",
+        "parseMode": "MarkdownV2",
+        "options": {
+          "disable_notification": false
+        }
+      },
+      "id": "telegram-notification-node",
+      "name": "Send Telegram Notification",
+      "type": "n8n-nodes-base.telegram",
+      "typeVersion": 1,
+      "position": [
+        1650,
+        100
+      ],
+      "continueOnFail": true,
+      "credentials": {
+        "telegramApi": {
+          "id": "telegram-credentials",
+          "name": "Telegram Bot"
+        }
+      }
+    },
     {
       "parameters": {
         "jsCode": "// AI Processing - Enhanced with OpenRouter Analysis\n// Riceve i dati elaborati da OpenRouter con analisi AI\n\nconst logData = $input.first().json;\n\n// Log di sicurezza: non esporre raw_log completo nei log\nconsole.log('AI Processing completed for log ID:', logData.client_id);\nconsole.log('Client:', logData.client_id);\nconsole.log('Severity:', logData.severity);\nconsole.log('AI Status:', logData.ai_status);\nconsole.log('AI Model:', logData.ai_model || 'N/A');\n\n// Se c'\u00e8 l'analisi AI, logga la sintesi\nif (logData.ai_analysis) {\n  console.log('AI Sintesi:', logData.ai_analysis.sintesi);\n  console.log('AI Comando suggerito:', logData.ai_analysis.comando || 'Nessuno');\n}\n\nreturn [{\n  json: {\n    status: 'ai_processing_complete',\n    client_id: logData.client_id,\n    hostname: logData.hostname,\n    severity: logData.severity,\n    ai_analysis: logData.ai_analysis,\n    ai_status: logData.ai_status,\n    ai_model: logData.ai_model,\n    timestamp: logData.ai_timestamp || new Date().toISOString()\n  }\n}];"
@@ -149,8 +174,8 @@
       "type": "n8n-nodes-base.code",
       "typeVersion": 2,
       "position": [
-        1650,
-        50
+        1850,
+        100
       ]
     },
     {
@@ -331,7 +356,7 @@
       "main": [
         [
           {
-            "node": "AI Processing",
+            "node": "Send Telegram Notification",
             "type": "main",
             "index": 0
           }
@@ -345,6 +370,17 @@
         ]
       ]
     },
+    "Send Telegram Notification": {
+      "main": [
+        [
+          {
+            "node": "AI Processing",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    },
     "Ensure Table SQL": {
       "main": [
         [