fix(completions): instantiate Slugger per file

Move Slugger instantiation inside the file loops to prevent
state leakage between files, as Slugger is stateful.

src/components/journal/completions.ts

@@ -81,12 +81,15 @@ async function scanClientSide(): Promise<JournalCompletions> {
   const links: LinkCompletion[] = [];
   const sparkTables: SparkTableCompletion[] = [];
   const tagRegex = /<md-dice[^>]*>\s*([\s\S]*?)\s*<\/md-dice>/gi;
-  const slugger = new Slugger();
 
   for (const filePath of paths) {
     const content = await getIndexedData(filePath);
     if (!content) continue;
 
+    // Fresh slugger per file so duplicate headers across files don't
+    // pollute each other.
+    const slugger = new Slugger();
+
     // Dice scan
     let match: RegExpExecArray | null;
     tagRegex.lastIndex = 0;