Wissensdatenbank: Markdown, FTS5-Suche, Sanitizing, UX

- Markdown-Rendering fuer Notizen (fett, kursiv, Ueberschriften, Listen, Code, Links)
- HTML-Sanitizing im Frontend und Backend (XSS-Schutz)
- FTS5 Volltextindex fuer schnelle Suche mit Ranking
- Kategorie-Loeschung zeigt Anzahl betroffener Eintraege

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/database.js

@@ -552,6 +552,43 @@ function createTables() {
     )
   `);
 
+  // Wissensmanagement - FTS5 Volltextsuche
+  try {
+    db.exec(`
+      CREATE VIRTUAL TABLE IF NOT EXISTS knowledge_fts USING fts5(
+        title, notes, content=knowledge_entries, content_rowid=id
+      )
+    `);
+
+    // Trigger: INSERT synchronisieren
+    db.exec(`
+      CREATE TRIGGER IF NOT EXISTS knowledge_fts_insert AFTER INSERT ON knowledge_entries BEGIN
+        INSERT INTO knowledge_fts(rowid, title, notes) VALUES (NEW.id, NEW.title, NEW.notes);
+      END
+    `);
+
+    // Trigger: DELETE synchronisieren
+    db.exec(`
+      CREATE TRIGGER IF NOT EXISTS knowledge_fts_delete AFTER DELETE ON knowledge_entries BEGIN
+        INSERT INTO knowledge_fts(knowledge_fts, rowid, title, notes) VALUES('delete', OLD.id, OLD.title, OLD.notes);
+      END
+    `);
+
+    // Trigger: UPDATE synchronisieren
+    db.exec(`
+      CREATE TRIGGER IF NOT EXISTS knowledge_fts_update AFTER UPDATE ON knowledge_entries BEGIN
+        INSERT INTO knowledge_fts(knowledge_fts, rowid, title, notes) VALUES('delete', OLD.id, OLD.title, OLD.notes);
+        INSERT INTO knowledge_fts(rowid, title, notes) VALUES (NEW.id, NEW.title, NEW.notes);
+      END
+    `);
+
+    // Initiales Befuellen der FTS-Tabelle
+    db.exec(`INSERT INTO knowledge_fts(knowledge_fts) VALUES('rebuild')`);
+    logger.info('Knowledge FTS5 Volltextindex erstellt/aktualisiert');
+  } catch (ftsError) {
+    logger.warn('FTS5 konnte nicht erstellt werden (evtl. nicht unterstuetzt):', ftsError.message);
+  }
+
   // Wissensmanagement - Anhänge
   db.exec(`
     CREATE TABLE IF NOT EXISTS knowledge_attachments (